From 3e553eaf605d405abc191b4b95cc69a903d6a757 Mon Sep 17 00:00:00 2001
From: Luca Palmieri <LukeMathWalker@users.noreply.github.com>
Date: Sun, 27 Sep 2020 17:09:42 +0100
Subject: [PATCH] Chapter04 (#9)

* Add chapter 4 code.

* Add logger middleware.

* Add env_logger.

* Instrumented.

* Test logs.

* Introduce instrument.

* Refactor handler.

* Use TracingLogger.

* Update.

* Fix linter error.
---
 Cargo.lock                                    | 223 +++++++++++++++++-
 Cargo.toml                                    |   2 +-
 chapter04/.env                                |   1 +
 chapter04/Cargo.toml                          |  36 +++
 chapter04/configuration.yaml                  |   7 +
 ...00823135036_create_subscriptions_table.sql |   8 +
 chapter04/scripts/init_db.sh                  |  40 ++++
 chapter04/src/configuration.rs                |  38 +++
 chapter04/src/lib.rs                          |   5 +
 chapter04/src/main.rs                         |  29 +++
 chapter04/src/routes/health_check.rs          |   5 +
 chapter04/src/routes/mod.rs                   |   5 +
 chapter04/src/routes/subscriptions.rs         |  56 +++++
 chapter04/src/startup.rs                      |  21 ++
 chapter04/src/telemetry.rs                    |  29 +++
 chapter04/tests/health_check.rs               | 143 +++++++++++
 16 files changed, 644 insertions(+), 4 deletions(-)
 create mode 100644 chapter04/.env
 create mode 100644 chapter04/Cargo.toml
 create mode 100644 chapter04/configuration.yaml
 create mode 100644 chapter04/migrations/20200823135036_create_subscriptions_table.sql
 create mode 100755 chapter04/scripts/init_db.sh
 create mode 100644 chapter04/src/configuration.rs
 create mode 100644 chapter04/src/lib.rs
 create mode 100644 chapter04/src/main.rs
 create mode 100644 chapter04/src/routes/health_check.rs
 create mode 100644 chapter04/src/routes/mod.rs
 create mode 100644 chapter04/src/routes/subscriptions.rs
 create mode 100644 chapter04/src/startup.rs
 create mode 100644 chapter04/src/telemetry.rs
 create mode 100644 chapter04/tests/health_check.rs

diff --git a/Cargo.lock b/Cargo.lock
index 822ff87..530a279 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -271,6 +271,14 @@ dependencies = [
  "memchr 2.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "ansi_term"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "anyhow"
 version = "1.0.32"
@@ -304,6 +312,16 @@ dependencies = [
  "num-traits 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "atty"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "hermit-abi 0.1.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.76 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.0.1"
@@ -449,6 +467,31 @@ dependencies = [
  "uuid 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "chapter04"
+version = "0.1.0"
+dependencies = [
+ "actix-rt 1.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "actix-web 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "anyhow 1.0.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "chrono 0.4.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "config 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "env_logger 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "reqwest 0.10.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.115 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sqlx 0.4.0-beta.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tokio 0.2.22 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-actix-web 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-bunyan-formatter 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-futures 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-log 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-subscriber 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "uuid 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "chrono"
 version = "0.4.15"
@@ -608,6 +651,18 @@ dependencies = [
  "syn 1.0.39 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "env_logger"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "atty 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "humantime 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "regex 1.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "termcolor 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "failure"
 version = "0.1.8"
@@ -774,6 +829,15 @@ dependencies = [
  "version_check 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "gethostname"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.76 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.1.14"
@@ -880,6 +944,14 @@ name = "httparse"
 version = "1.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "humantime"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "quick-error 1.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "hyper"
 version = "0.13.7"
@@ -1051,6 +1123,14 @@ name = "match_cfg"
 version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "matchers"
+version = "0.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "regex-automata 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "matches"
 version = "0.1.8"
@@ -1396,6 +1476,15 @@ dependencies = [
  "thread_local 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "regex-automata"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "byteorder 1.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "regex-syntax 0.6.18 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "regex-syntax"
 version = "0.6.18"
@@ -1566,6 +1655,14 @@ dependencies = [
  "opaque-debug 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "sharded-slab"
+version = "0.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "signal-hook-registry"
 version = "1.2.1"
@@ -1741,6 +1838,14 @@ dependencies = [
  "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "termcolor"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi-util 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "thiserror"
 version = "1.0.20"
@@ -1877,17 +1982,104 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
- "tracing-core 0.1.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-attributes 0.1.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-core 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "tracing-actix-web"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "actix-web 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-futures 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "uuid 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "tracing-attributes"
+version = "0.1.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 1.0.19 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.39 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "tracing-bunyan-formatter"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "chrono 0.4.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "gethostname 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.115 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.57 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-core 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-log 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-subscriber 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "tracing-core"
-version = "0.1.15"
+version = "0.1.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "tracing-futures"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "pin-project 0.4.23 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-core 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "tracing-serde"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "serde 1.0.115 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-core 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "tracing-subscriber"
+version = "0.2.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "ansi_term 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "chrono 0.4.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "matchers 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "regex 1.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.115 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.57 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sharded-slab 0.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 1.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "thread_local 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-core 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-log 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tracing-serde 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "trust-dns-proto"
 version = "0.18.0-alpha.2"
@@ -2116,6 +2308,14 @@ name = "winapi-i686-pc-windows-gnu"
 version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "winapi-util"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "winapi-x86_64-pc-windows-gnu"
 version = "0.4.0"
@@ -2173,11 +2373,13 @@ dependencies = [
 "checksum adler 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "ee2a4ec343196209d6594e19543ae87a39f96d5534d7174822a3ad825dd6ed7e"
 "checksum ahash 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)" = "e8fd72866655d1904d6b0997d0b07ba561047d070fbe29de039031c641b61217"
 "checksum aho-corasick 0.7.13 (registry+https://github.com/rust-lang/crates.io-index)" = "043164d8ba5c4c3035fec9bbee8647c0261d788f3474306f93bb65901cae0e86"
+"checksum ansi_term 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d52a9bb7ec0cf484c551830a7ce27bd20d67eac647e1befb56b0be4ee39a55d2"
 "checksum anyhow 1.0.32 (registry+https://github.com/rust-lang/crates.io-index)" = "6b602bfe940d21c130f3895acd65221e8a61270debe89d628b9cb4e3ccb8569b"
 "checksum arc-swap 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)" = "4d25d88fd6b8041580a654f9d0c581a047baee2b3efee13275f2fc392fc75034"
 "checksum arrayvec 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "cff77d8686867eceff3105329d4698d96c2391c176d5d03adc90c7389162b5b8"
 "checksum async-trait 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)" = "6e1a4a2f97ce50c9d0282c1468816208588441492b40d813b2e0419c22c05e7f"
 "checksum atoi 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e0afb7287b68575f5ca0e5c7e40191cbd4be59d325781f46faa603e176eaef47"
+"checksum atty 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)" = "d9b39be18770d11421cdb1b9947a45dd3f37e93092cbf377614828a319d5fee8"
 "checksum autocfg 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 "checksum awc 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d7601d4d1d7ef2335d6597a41b5fe069f6ab799b85f53565ab390e7b7065aac5"
 "checksum backtrace 0.3.50 (registry+https://github.com/rust-lang/crates.io-index)" = "46254cf2fdcdf1badb5934448c1bcbe046a56537b3987d96c51a7afc5d03f293"
@@ -2214,6 +2416,7 @@ dependencies = [
 "checksum either 1.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "cd56b59865bce947ac5958779cfa508f6c3b9497cc762b7e24a12d11ccde2c4f"
 "checksum encoding_rs 0.8.23 (registry+https://github.com/rust-lang/crates.io-index)" = "e8ac63f94732332f44fe654443c46f6375d1939684c17b0afb6cb56b0456e171"
 "checksum enum-as-inner 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "7c5f0096a91d210159eceb2ff5e1c4da18388a170e1e3ce948aac9c8fdbbf595"
+"checksum env_logger 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)" = "44533bbbb3bb3c1fa17d9f2e4e38bbbaf8396ba82193c4cb1b6445d711445d36"
 "checksum failure 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)" = "d32e9bd16cc02eae7db7ef620b392808b89f6a5e16bb3497d159c6b92a0f4f86"
 "checksum failure_derive 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)" = "aa4da3c766cd7a0db8242e326e9e4e081edd567072893ed320008189715366a4"
 "checksum flate2 1.0.17 (registry+https://github.com/rust-lang/crates.io-index)" = "766d0e77a2c1502169d4a93ff3b8c15a71fd946cd0126309752104e5f3c46d94"
@@ -2233,6 +2436,7 @@ dependencies = [
 "checksum futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "8764574ff08b701a084482c3c7031349104b07ac897393010494beaa18ce32c6"
 "checksum fxhash 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "c31b6d751ae2c7f11320402d34e41349dd1016f8d5d45e48c4312bc8625af50c"
 "checksum generic-array 0.14.4 (registry+https://github.com/rust-lang/crates.io-index)" = "501466ecc8a30d1d3b7fc9229b122b2ce8ed6e9d9223f1138d4babb253e51817"
+"checksum gethostname 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "e692e296bfac1d2533ef168d0b60ff5897b8b70a4009276834014dd8924cc028"
 "checksum getrandom 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)" = "7abc8dd8451921606d809ba32e95b6111925cd2906060d2dcc29c070220503eb"
 "checksum gimli 0.22.0 (registry+https://github.com/rust-lang/crates.io-index)" = "aaf91faf136cb47367fa430cd46e37a788775e7fa104f8b4bcb3861dc389b724"
 "checksum h2 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "993f9e0baeed60001cf565546b0d3dbe6a6ad23f2bd31644a133c641eccf6d53"
@@ -2245,6 +2449,7 @@ dependencies = [
 "checksum http 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "28d569972648b2c512421b5f2a405ad6ac9666547189d0c5477a3f200f3e02f9"
 "checksum http-body 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "13d5ff830006f7646652e057693569bfe0d51760c0085a071769d142a205111b"
 "checksum httparse 1.3.4 (registry+https://github.com/rust-lang/crates.io-index)" = "cd179ae861f0c2e53da70d892f5f3029f9594be0c41dc5269cd371691b1dc2f9"
+"checksum humantime 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "df004cfca50ef23c36850aaaa59ad52cc70d0e90243c3c7737a4dd32dc7a3c4f"
 "checksum hyper 0.13.7 (registry+https://github.com/rust-lang/crates.io-index)" = "3e68a8dd9716185d9e64ea473ea6ef63529252e3e27623295a0378a19665d5eb"
 "checksum hyper-tls 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "d979acc56dcb5b8dddba3917601745e877576475aa046df3226eabdecef78eed"
 "checksum idna 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "02e2673c30ee86b5b96a9cb52ad15718aa1f966f5ab9ad54a8b95d5ca33120a9"
@@ -2266,6 +2471,7 @@ dependencies = [
 "checksum lru-cache 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "31e24f1ad8321ca0e8a1e0ac13f23cb668e6f5466c2c57319f6a5cf1cc8e3b1c"
 "checksum maplit 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "3e2e65a1a2e43cfcb47a895c4c8b10d1f4a61097f9f254f183aee60cad9c651d"
 "checksum match_cfg 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ffbee8634e0d45d258acb448e7eaab3fce7a0a467395d4d9f228e3c1f01fb2e4"
+"checksum matchers 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "f099785f7595cc4b4553a174ce30dd7589ef93391ff414dbb67f62392b9e0ce1"
 "checksum matches 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)" = "7ffc5c5338469d4d3ea17d269fa8ea3512ad247247c30bd2df69e68309ed0a08"
 "checksum maybe-uninit 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "60302e4db3a61da70c0cb7991976248362f30319e88850c487b9b95bbf059e00"
 "checksum md-5 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)" = "7b5a279bb9607f9f53c22d496eade00d138d1bdcccd07d74650387cf94942a15"
@@ -2308,6 +2514,7 @@ dependencies = [
 "checksum rand_hc 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ca3129af7b92a17112d59ad498c6f81eaf463253766b90396d39ea7a39d6613c"
 "checksum redox_syscall 0.1.57 (registry+https://github.com/rust-lang/crates.io-index)" = "41cc0f7e4d5d4544e8861606a285bb08d3e70712ccc7d2b84d7c0ccfaf4b05ce"
 "checksum regex 1.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "9c3780fcf44b193bc4d09f36d2a3c87b251da4a046c87795a0d35f4f927ad8e6"
+"checksum regex-automata 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)" = "ae1ded71d66a4a97f5e961fd0cb25a5f366a42a41570d16a763a69c092c26ae4"
 "checksum regex-syntax 0.6.18 (registry+https://github.com/rust-lang/crates.io-index)" = "26412eb97c6b088a6997e05f69403a802a92d520de2f8e63c2b65f9e0f47c4e8"
 "checksum remove_dir_all 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3acd125665422973a33ac9d3dd2df85edad0f4ae9b00dafb1a05e43a9f5ef8e7"
 "checksum reqwest 0.10.7 (registry+https://github.com/rust-lang/crates.io-index)" = "12427a5577082c24419c9c417db35cfeb65962efc7675bb6b0d5f1f9d315bfe6"
@@ -2325,6 +2532,7 @@ dependencies = [
 "checksum sha-1 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)" = "170a36ea86c864a3f16dd2687712dd6646f7019f301e57537c7f4dc9f5916770"
 "checksum sha1 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "2579985fda508104f7587689507983eadd6a6e84dd35d6d115361f530916fa0d"
 "checksum sha2 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2933378ddfeda7ea26f48c555bdad8bb446bf8a3d17832dc83e380d444cfb8c1"
+"checksum sharded-slab 0.0.9 (registry+https://github.com/rust-lang/crates.io-index)" = "06d5a3f5166fb5b42a5439f2eee8b9de149e235961e3eb21c5808fc3ea17ff3e"
 "checksum signal-hook-registry 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a3e12110bc539e657a646068aaf5eb5b63af9d0c1f7b29c97113fad80e15f035"
 "checksum slab 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
 "checksum smallvec 1.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "fbee7696b84bbf3d89a1c2eccff0850e3047ed46bfcd2e92c29a2d074d57e252"
@@ -2340,6 +2548,7 @@ dependencies = [
 "checksum syn 1.0.39 (registry+https://github.com/rust-lang/crates.io-index)" = "891d8d6567fe7c7f8835a3a98af4208f3846fba258c1bc3c31d6e506239f11f9"
 "checksum synstructure 0.12.4 (registry+https://github.com/rust-lang/crates.io-index)" = "b834f2d66f734cb897113e34aaff2f1ab4719ca946f9a7358dba8f8064148701"
 "checksum tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7a6e24d9338a0a5be79593e2fa15a648add6138caa803e2d5bc782c371732ca9"
+"checksum termcolor 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "bb6bfa289a4d7c5766392812c0a1f4c1ba45afa1ad47803c11e1f407d846d75f"
 "checksum thiserror 1.0.20 (registry+https://github.com/rust-lang/crates.io-index)" = "7dfdd070ccd8ccb78f4ad66bf1982dc37f620ef696c6b5028fe2ed83dd3d0d08"
 "checksum thiserror-impl 1.0.20 (registry+https://github.com/rust-lang/crates.io-index)" = "bd80fc12f73063ac132ac92aceea36734f04a1d93c1240c6944e23a3b8841793"
 "checksum thread_local 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d40c6d1b69745a6ec6fb1ca717914848da4b44ae29d9b3080cbee91d72a69b14"
@@ -2354,7 +2563,14 @@ dependencies = [
 "checksum tokio-util 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "be8242891f2b6cbef26a2d7e8605133c2c554cd35b3e4948ea892d6d68436499"
 "checksum tower-service 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e987b6bf443f4b5b3b6f38704195592cca41c5bb7aedd3c3693c7081f8289860"
 "checksum tracing 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)" = "6d79ca061b032d6ce30c660fded31189ca0b9922bf483cd70759f13a2d86786c"
-"checksum tracing-core 0.1.15 (registry+https://github.com/rust-lang/crates.io-index)" = "4f0e00789804e99b20f12bc7003ca416309d28a6f495d6af58d1e2c2842461b5"
+"checksum tracing-actix-web 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d9e2e3bdcd192ec7786b47addd10f66fbc7c06d32f1757ddaa31e28eec045aea"
+"checksum tracing-attributes 0.1.11 (registry+https://github.com/rust-lang/crates.io-index)" = "80e0ccfc3378da0cce270c946b676a376943f5cd16aeba64568e7939806f4ada"
+"checksum tracing-bunyan-formatter 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "8d8dfd28e9ee6d79937f139ae4f112fa2172018cfdf111c0dac1f3f8c6912053"
+"checksum tracing-core 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)" = "5bcf46c1f1f06aeea2d6b81f3c863d0930a596c86ad1920d4e5bad6dd1d7119a"
+"checksum tracing-futures 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)" = "ab7bb6f14721aa00656086e9335d363c5c8747bae02ebe32ea2c7dece5689b4c"
+"checksum tracing-log 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "5e0f8c7178e13481ff6765bd169b33e8d554c5d2bbede5e32c356194be02b9b9"
+"checksum tracing-serde 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "fb65ea441fbb84f9f6748fd496cf7f63ec9af5bca94dd86456978d055e8eb28b"
+"checksum tracing-subscriber 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)" = "82bb5079aa76438620837198db8a5c529fb9878c730bc2b28179b0241cf04c10"
 "checksum trust-dns-proto 0.18.0-alpha.2 (registry+https://github.com/rust-lang/crates.io-index)" = "2a7f3a2ab8a919f5eca52a468866a67ed7d3efa265d48a652a9a3452272b413f"
 "checksum trust-dns-resolver 0.18.0-alpha.2 (registry+https://github.com/rust-lang/crates.io-index)" = "6f90b1502b226f8b2514c6d5b37bafa8c200d7ca4102d57dc36ee0f3b7a04a2f"
 "checksum try-lock 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "59547bce71d9c38b83d9c0e92b6066c4253371f15005def0c30d9657f50c7642"
@@ -2383,6 +2599,7 @@ dependencies = [
 "checksum winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
 "checksum winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2d315eee3b34aca4797b2da6b13ed88266e6d612562a0c46390af8299fc699bc"
 "checksum winapi-i686-pc-windows-gnu 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+"checksum winapi-util 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
 "checksum winapi-x86_64-pc-windows-gnu 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 "checksum winreg 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "b2986deb581c4fe11b621998a5e53361efe6b48a151178d0cd9eeffa4dc6acc9"
 "checksum winreg 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0120db82e8a1e0b9fb3345a539c478767c0048d842860994d96113d5b667bd69"
diff --git a/Cargo.toml b/Cargo.toml
index 912af18..5b8f01e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,2 +1,2 @@
 [workspace]
-members = ["chapter03-0", "chapter03-1"]
+members = ["chapter03-0", "chapter03-1", "chapter04"]
diff --git a/chapter04/.env b/chapter04/.env
new file mode 100644
index 0000000..88cfb53
--- /dev/null
+++ b/chapter04/.env
@@ -0,0 +1 @@
+DATABASE_URL="postgres://postgres:password@localhost:5432/newsletter"
diff --git a/chapter04/Cargo.toml b/chapter04/Cargo.toml
new file mode 100644
index 0000000..fbde63f
--- /dev/null
+++ b/chapter04/Cargo.toml
@@ -0,0 +1,36 @@
+[package]
+name = "chapter04"
+version = "0.1.0"
+authors = ["LukeMathWalker <rust@lpalmieri.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[lib]
+path = "src/lib.rs"
+
+[[bin]]
+path = "src/main.rs"
+name = "chapter04"
+
+[dependencies]
+actix-web = "2.0.0"
+actix-rt = "1.1.1"
+tokio = "0.2.22"
+serde = "1.0.115"
+config = { version = "0.10.1", default-features = false, features = ["yaml"] }
+sqlx = { version = "0.4.0-beta.1", default-features = false, features = [ "runtime-tokio", "macros", "postgres", "uuid", "chrono", "migrate"] }
+anyhow = "1.0.32"
+uuid = { version = "0.8.1", features = ["v4"] }
+chrono = "0.4.15"
+env_logger = "0.7.1"
+log = "0.4.11"
+tracing = "0.1.19"
+tracing-futures = "0.2.4"
+tracing-subscriber = { version = "0.2.12", features = ["registry", "env-filter"] }
+tracing-bunyan-formatter = "0.1.6"
+tracing-log = "0.1.1"
+tracing-actix-web = "0.1.1"
+
+[dev-dependencies]
+reqwest = { version = "0.10.7", features = ["json"] }
+lazy_static = "1.4.0"
diff --git a/chapter04/configuration.yaml b/chapter04/configuration.yaml
new file mode 100644
index 0000000..04dc5ef
--- /dev/null
+++ b/chapter04/configuration.yaml
@@ -0,0 +1,7 @@
+application_port: 8000
+database:
+  host: "localhost"
+  port: 5432
+  username: "postgres"
+  password: "password"
+  database_name: "newsletter"
\ No newline at end of file
diff --git a/chapter04/migrations/20200823135036_create_subscriptions_table.sql b/chapter04/migrations/20200823135036_create_subscriptions_table.sql
new file mode 100644
index 0000000..2c0d262
--- /dev/null
+++ b/chapter04/migrations/20200823135036_create_subscriptions_table.sql
@@ -0,0 +1,8 @@
+-- Create Subscriptions Table
+CREATE TABLE subscriptions(
+   id uuid NOT NULL,
+   PRIMARY KEY (id),
+   email TEXT NOT NULL UNIQUE,
+   name TEXT NOT NULL,
+   subscribed_at timestamptz NOT NULL
+);
\ No newline at end of file
diff --git a/chapter04/scripts/init_db.sh b/chapter04/scripts/init_db.sh
new file mode 100755
index 0000000..cc1df04
--- /dev/null
+++ b/chapter04/scripts/init_db.sh
@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -x
+set -eo pipefail
+
+# Check if a custom user has been set, otherwise default to 'postgres'
+DB_USER=${POSTGRES_USER:=postgres}
+# Check if a custom password has been set, otherwise default to 'password'
+DB_PASSWORD="${POSTGRES_PASSWORD:=password}"
+# Check if a custom password has been set, otherwise default to 'newsletter'
+DB_NAME="${POSTGRES_DB:=newsletter}"
+# Check if a custom port has been set, otherwise default to '5432'
+DB_PORT="${POSTGRES_PORT:=5432}"
+
+# Allow to skip Docker if a dockerized Postgres database is already running
+if [[ -z "${SKIP_DOCKER}" ]]
+then
+  # Launch postgres using Docker
+  docker run \
+      -e POSTGRES_USER=${DB_USER} \
+      -e POSTGRES_PASSWORD=${DB_PASSWORD} \
+      -e POSTGRES_DB=${DB_NAME} \
+      -p "${DB_PORT}":5432 \
+      -d postgres \
+      postgres -N 1000
+      # ^ Increased maximum number of connections for testing purposes
+fi
+
+# Keep pinging Postgres until it's ready to accept commands
+until PGPASSWORD="${DB_PASSWORD}" psql -h "localhost" -U "${DB_USER}" -p "${DB_PORT}" -d "postgres" -c '\q'; do
+  >&2 echo "Postgres is still unavailable - sleeping"
+  sleep 1
+done
+
+>&2 echo "Postgres is up and running on port ${DB_PORT} - running migrations now!"
+
+export DATABASE_URL=postgres://${DB_USER}:${DB_PASSWORD}@localhost:${DB_PORT}/${DB_NAME}
+sqlx database create
+sqlx migrate run
+
+>&2 echo "Postgres has been migrated, ready to go!"
diff --git a/chapter04/src/configuration.rs b/chapter04/src/configuration.rs
new file mode 100644
index 0000000..3ad6da7
--- /dev/null
+++ b/chapter04/src/configuration.rs
@@ -0,0 +1,38 @@
+#[derive(serde::Deserialize)]
+pub struct Settings {
+    pub database: DatabaseSettings,
+    pub application_port: u16,
+}
+
+#[derive(serde::Deserialize)]
+pub struct DatabaseSettings {
+    pub username: String,
+    pub password: String,
+    pub port: u16,
+    pub host: String,
+    pub database_name: String,
+}
+
+impl DatabaseSettings {
+    pub fn connection_string(&self) -> String {
+        format!(
+            "postgres://{}:{}@{}:{}/{}",
+            self.username, self.password, self.host, self.port, self.database_name
+        )
+    }
+
+    pub fn connection_string_without_db(&self) -> String {
+        format!(
+            "postgres://{}:{}@{}:{}",
+            self.username, self.password, self.host, self.port
+        )
+    }
+}
+
+pub fn get_configuration() -> Result<Settings, config::ConfigError> {
+    let mut settings = config::Config::default();
+
+    settings.merge(config::File::with_name("configuration"))?;
+
+    settings.try_into()
+}
diff --git a/chapter04/src/lib.rs b/chapter04/src/lib.rs
new file mode 100644
index 0000000..5d8e21e
--- /dev/null
+++ b/chapter04/src/lib.rs
@@ -0,0 +1,5 @@
+#![allow(clippy::toplevel_ref_arg)]
+pub mod configuration;
+pub mod routes;
+pub mod startup;
+pub mod telemetry;
diff --git a/chapter04/src/main.rs b/chapter04/src/main.rs
new file mode 100644
index 0000000..a7a516b
--- /dev/null
+++ b/chapter04/src/main.rs
@@ -0,0 +1,29 @@
+use anyhow::Context;
+use chapter04::configuration::get_configuration;
+use chapter04::startup::run;
+use chapter04::telemetry::{get_subscriber, init_subscriber};
+use sqlx::postgres::PgPool;
+use std::net::TcpListener;
+
+#[actix_rt::main]
+async fn main() -> Result<(), anyhow::Error> {
+    let subscriber = get_subscriber("zero2prod".into(), "info".into());
+    init_subscriber(subscriber);
+
+    let configuration = get_configuration().expect("Failed to read configuration.");
+    let connection_pool = PgPool::connect(&configuration.database.connection_string())
+        .await
+        .map_err(anyhow::Error::from)
+        .with_context(|| "Failed to connect to Postgres.")?;
+
+    // Here we choose to bind explicitly to localhost, 127.0.0.1, for security
+    // reasons. This binding may cause issues in some environments. For example,
+    // it causes connectivity issues running in WSL2, where you cannot reach the
+    // server when it is bound to WSL2's localhost interface. As a workaround,
+    // you can choose to bind to all interfaces, 0.0.0.0, instead, but be aware
+    // of the security implications when you expose the server on all interfaces.
+    let address = format!("127.0.0.1:{}", configuration.application_port);
+    let listener = TcpListener::bind(address)?;
+    run(listener, connection_pool)?.await?;
+    Ok(())
+}
diff --git a/chapter04/src/routes/health_check.rs b/chapter04/src/routes/health_check.rs
new file mode 100644
index 0000000..d7eb4e0
--- /dev/null
+++ b/chapter04/src/routes/health_check.rs
@@ -0,0 +1,5 @@
+use actix_web::HttpResponse;
+
+pub async fn health_check() -> HttpResponse {
+    HttpResponse::Ok().finish()
+}
diff --git a/chapter04/src/routes/mod.rs b/chapter04/src/routes/mod.rs
new file mode 100644
index 0000000..90ffeed
--- /dev/null
+++ b/chapter04/src/routes/mod.rs
@@ -0,0 +1,5 @@
+mod health_check;
+mod subscriptions;
+
+pub use health_check::*;
+pub use subscriptions::*;
diff --git a/chapter04/src/routes/subscriptions.rs b/chapter04/src/routes/subscriptions.rs
new file mode 100644
index 0000000..e5a86be
--- /dev/null
+++ b/chapter04/src/routes/subscriptions.rs
@@ -0,0 +1,56 @@
+use actix_web::{web, HttpResponse};
+use chrono::Utc;
+use sqlx::PgPool;
+use uuid::Uuid;
+
+#[derive(serde::Deserialize)]
+pub struct SubscribeRequest {
+    email: String,
+    name: String,
+}
+
+#[tracing::instrument(
+    name = "Adding a new subscriber",
+    skip(payload, pool),
+    fields(
+        request_id=%Uuid::new_v4(),
+        email = %payload.email,
+        name = %payload.name
+    )
+)]
+pub async fn subscribe(
+    payload: web::Form<SubscribeRequest>,
+    pool: web::Data<PgPool>,
+) -> Result<HttpResponse, HttpResponse> {
+    insert_subscriber(&pool, &payload)
+        .await
+        .map_err(|_| HttpResponse::InternalServerError().finish())?;
+    Ok(HttpResponse::Ok().finish())
+}
+
+#[tracing::instrument(
+    name = "Saving new subscriber details in the database",
+    skip(payload, pool)
+)]
+pub async fn insert_subscriber(
+    pool: &PgPool,
+    payload: &SubscribeRequest,
+) -> Result<(), sqlx::Error> {
+    sqlx::query!(
+        r#"
+    INSERT INTO subscriptions (id, email, name, subscribed_at)
+    VALUES ($1, $2, $3, $4)
+            "#,
+        Uuid::new_v4(),
+        payload.email,
+        payload.name,
+        Utc::now()
+    )
+    .execute(pool)
+    .await
+    .map_err(|e| {
+        tracing::error!("Failed to execute query: {:?}", e);
+        e
+    })?;
+    Ok(())
+}
diff --git a/chapter04/src/startup.rs b/chapter04/src/startup.rs
new file mode 100644
index 0000000..d091772
--- /dev/null
+++ b/chapter04/src/startup.rs
@@ -0,0 +1,21 @@
+use crate::routes::{health_check, subscribe};
+use actix_web::dev::Server;
+use actix_web::web::Data;
+use actix_web::{web, App, HttpServer};
+use sqlx::PgPool;
+use std::net::TcpListener;
+use tracing_actix_web::TracingLogger;
+
+pub fn run(listener: TcpListener, db_pool: PgPool) -> Result<Server, std::io::Error> {
+    let db_pool = Data::new(db_pool);
+    let server = HttpServer::new(move || {
+        App::new()
+            .wrap(TracingLogger)
+            .route("/health_check", web::get().to(health_check))
+            .route("/subscriptions", web::post().to(subscribe))
+            .app_data(db_pool.clone())
+    })
+    .listen(listener)?
+    .run();
+    Ok(server)
+}
diff --git a/chapter04/src/telemetry.rs b/chapter04/src/telemetry.rs
new file mode 100644
index 0000000..27168fb
--- /dev/null
+++ b/chapter04/src/telemetry.rs
@@ -0,0 +1,29 @@
+use tracing::subscriber::set_global_default;
+use tracing::Subscriber;
+use tracing_bunyan_formatter::{BunyanFormattingLayer, JsonStorageLayer};
+use tracing_log::LogTracer;
+use tracing_subscriber::{layer::SubscriberExt, EnvFilter, Registry};
+
+/// Compose multiple layers into a `tracing`'s subscriber.
+///
+/// # Implementation Notes
+///
+/// We are using `impl Subscriber` as return type to avoid having to spell out the actual
+/// type of the returned subscriber, which is indeed quite complex.
+pub fn get_subscriber(name: String, env_filter: String) -> impl Subscriber + Sync + Send {
+    let env_filter =
+        EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new(env_filter));
+    let formatting_layer = BunyanFormattingLayer::new(name, std::io::stdout);
+    Registry::default()
+        .with(env_filter)
+        .with(JsonStorageLayer)
+        .with(formatting_layer)
+}
+
+/// Register a subscriber as global default to process span data.
+///
+/// It should only be called once!
+pub fn init_subscriber(subscriber: impl Subscriber + Sync + Send) {
+    LogTracer::init().expect("Failed to set logger");
+    set_global_default(subscriber).expect("Failed to set subscriber");
+}
diff --git a/chapter04/tests/health_check.rs b/chapter04/tests/health_check.rs
new file mode 100644
index 0000000..c0ac230
--- /dev/null
+++ b/chapter04/tests/health_check.rs
@@ -0,0 +1,143 @@
+use chapter04::configuration::{get_configuration, DatabaseSettings};
+use chapter04::startup::run;
+use chapter04::telemetry::{get_subscriber, init_subscriber};
+use sqlx::{Connection, Executor, PgConnection, PgPool};
+use std::net::TcpListener;
+use uuid::Uuid;
+
+// Ensure that the `tracing` stack is only initialised once using `lazy_static`
+lazy_static::lazy_static! {
+    static ref TRACING: () = {
+        let filter = if std::env::var("TEST_LOG").is_ok() { "debug" } else { "" };
+        let subscriber = get_subscriber("test".into(), filter.into());
+        init_subscriber(subscriber);
+    };
+}
+
+pub struct TestApp {
+    pub address: String,
+    pub db_pool: PgPool,
+}
+
+async fn spawn_app() -> TestApp {
+    // The first time `initialize` is invoked the code in `TRACING` is executed.
+    // All other invocations will instead skip execution.
+    lazy_static::initialize(&TRACING);
+
+    let listener = TcpListener::bind("127.0.0.1:0").expect("Failed to bind random port");
+    // We retrieve the port assigned to us by the OS
+    let port = listener.local_addr().unwrap().port();
+    let address = format!("http://127.0.0.1:{}", port);
+
+    let mut configuration = get_configuration().expect("Failed to read configuration.");
+    configuration.database.database_name = Uuid::new_v4().to_string();
+    let connection_pool = configure_database(&configuration.database).await;
+
+    let server = run(listener, connection_pool.clone()).expect("Failed to bind address");
+    let _ = tokio::spawn(server);
+    TestApp {
+        address,
+        db_pool: connection_pool,
+    }
+}
+
+pub async fn configure_database(config: &DatabaseSettings) -> PgPool {
+    // Create database
+    let mut connection = PgConnection::connect(&config.connection_string_without_db())
+        .await
+        .expect("Failed to connect to Postgres");
+    connection
+        .execute(&*format!(r#"CREATE DATABASE "{}";"#, config.database_name))
+        .await
+        .expect("Failed to create database.");
+
+    // Migrate database
+    let connection_pool = PgPool::connect(&config.connection_string())
+        .await
+        .expect("Failed to connect to Postgres.");
+    sqlx::migrate!("./migrations")
+        .run(&connection_pool)
+        .await
+        .expect("Failed to migrate the database");
+
+    connection_pool
+}
+
+#[actix_rt::test]
+async fn health_check_works() {
+    // Arrange
+    let app = spawn_app().await;
+    let client = reqwest::Client::new();
+
+    // Act
+    let response = client
+        // Use the returned application address
+        .get(&format!("{}/health_check", &app.address))
+        .send()
+        .await
+        .expect("Failed to execute request.");
+
+    // Assert
+    assert!(response.status().is_success());
+    assert_eq!(Some(0), response.content_length());
+}
+
+#[actix_rt::test]
+async fn subscribe_returns_a_200_for_valid_form_data() {
+    // Arrange
+    let app = spawn_app().await;
+    let client = reqwest::Client::new();
+    let body = "name=le%20guin&email=ursula_le_guin%40gmail.com";
+
+    // Act
+    let response = client
+        .post(&format!("{}/subscriptions", &app.address))
+        .header("Content-Type", "application/x-www-form-urlencoded")
+        .body(body)
+        .send()
+        .await
+        .expect("Failed to execute request.");
+
+    // Assert
+    assert_eq!(200, response.status().as_u16());
+
+    let saved = sqlx::query!("SELECT email, name FROM subscriptions",)
+        .fetch_one(&app.db_pool)
+        .await
+        .expect("Failed to fetch saved subscription.");
+
+    assert_eq!(saved.email, "ursula_le_guin@gmail.com");
+    assert_eq!(saved.name, "le guin");
+}
+
+#[actix_rt::test]
+async fn subscribe_returns_a_400_when_data_is_missing() {
+    // Arrange
+    let app = spawn_app().await;
+    let client = reqwest::Client::new();
+    let test_cases = vec![
+        ("name=le%20guin", "missing the email"),
+        ("email=ursula_le_guin%40gmail.com", "missing the name"),
+        ("", "missing both name and email"),
+    ];
+
+    for (invalid_body, error_message) in test_cases {
+        // Act
+        let response = client
+            .post(&format!("{}/subscriptions", &app.address))
+            .header("Content-Type", "application/x-www-form-urlencoded")
+            .body(invalid_body)
+            .send()
+            .await
+            .expect("Failed to execute request.");
+
+        // Assert
+        assert_eq!(
+            400,
+            response.status().as_u16(),
+            // Additional customised error message on test failure
+            "The API did not fail with 400 Bad Request when the payload was {}.",
+            error_message
+        );
+    }
+}