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138 lines
4.9 KiB
Markdown
138 lines
4.9 KiB
Markdown
---
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title: '[Community] Podman image build with sigstore'
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description: Build images in Podman with sigstore signature checking and signing
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slug: podman-image-build-sigstore
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authors:
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- name: handlebargh
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url: https://github.com/handlebargh
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image_url: https://github.com/handlebargh.png
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hide_table_of_contents: false
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tags: [community, image, podman, sigstore, signature]
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---
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<!-- cspell:ignore BQVUJ Containerfile cosing distroless fulcio keypair nonroot QVRFLS rekor skopeo -->
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This example shows how to build a container image with podman while verifying the base image and signing the resulting image.
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The image being pulled uses a keyless signature, while the image being built will be signed by a pre-generated private key.
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## Prerequisites
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### Generate signing keypair
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You can use cosing or skopeo to generate the keypair.
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Using skopeo:
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```bash
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skopeo generate-sigstore-key --output-prefix myKey
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```
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This command will generate a `myKey.private` and a `myKey.pub` keyfile.
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Store the `myKey.private` as secret in Woodpecker. In the example below, the secret is called `sigstore_private_key`
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### Configure hosts pulling the resulting image
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See [here](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/building_running_and_managing_containers/assembly_signing-container-images_building-running-and-managing-containers#proc_verifying-sigstore-image-signatures-using-a-public-key_assembly_signing-container-images) on how to configure the hosts pulling the built and signed image.
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## Repository structure
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Consider the `Makefile` having a `build` target that will be used in the following workflow.
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This target yields a Go binary with the filename `app` that will be placed in the root directory.
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```bash
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.
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├── Containerfile
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├── main.go
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├── go.mod
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├── go.sum
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├── .woodpecker.yml
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└── Makefile
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```
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### Containerfile
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The Containerfile refers to the base image that will be verified when pulled.
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```dockerfile
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FROM gcr.io/distroless/static-debian12:nonroot
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COPY app /app
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CMD ["/app"]
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```
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### Woodpecker workflow
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```yaml
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steps:
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build:
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image: docker.io/library/golang:1.21
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pull: true
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commands:
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- make build
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publish:
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image: quay.io/podman/stable:latest
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# Caution: This image is built daily. It might fill up your image store quickly.
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pull: true
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# Fill in the trusted checkbox in Woodpecker's settings as well
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privileged: true
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commands:
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# Configure podman to use sigstore attachments for both, the registry you pull from and the registry you push to.
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- |
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printf "docker:
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registry.gitlab.com:
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use-sigstore-attachments: true
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gcr.io:
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use-sigstore-attachments: true" >> /etc/containers/registries.d/default.yaml
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# At pull, check the keyless sigstore signature of the distroless image.
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# This is a very strict container policy. It allows pulling from gcr.io/distroless only. Every other registry will be rejected.
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# See https://github.com/containers/image/blob/main/docs/containers-policy.json.5.md for more information.
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# fulcio CA crt obtained from https://github.com/sigstore/sigstore/blob/main/pkg/tuf/repository/targets/fulcio_v1.crt.pem
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# rekor public key obtained from https://github.com/sigstore/sigstore/blob/main/pkg/tuf/repository/targets/rekor.pub
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# crt/key data is base64 encoded. --> echo "$CERT" | base64
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- |
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printf '{
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"default": [
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{
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"type": "reject"
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}
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],
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"transports": {
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"docker": {
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"gcr.io/distroless": [
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{
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"type": "sigstoreSigned",
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"fulcio": {
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"caData": "LS0tLS1CRUdJTiBDR...QVRFLS0tLS0K",
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"oidcIssuer": "https://accounts.google.com",
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"subjectEmail": "keyless@distroless.iam.gserviceaccount.com"
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},
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"rekorPublicKeyData": "LS0tLS1CRUdJTiBQVUJ...lDIEtFWS0tLS0tCg==",
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"signedIdentity": { "type": "matchRepository" }
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}
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]
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},
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"docker-daemon": {
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"": [
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{
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"type": "reject"
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}
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]
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}
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}
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}' > /etc/containers/policy.json
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# Use this key to sign the built image at push.
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- echo "$SIGSTORE_PRIVATE_KEY" > key.private
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# Login at the registry
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- echo $REGISTRY_LOGIN_TOKEN | podman login -u <username> --password-stdin registry.gitlab.com
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# Build the container image
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- podman build --tag registry.gitlab.com/<namespace>/<repository_name>/<image_name>:latest .
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# Sign and push the image
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- podman push --sign-by-sigstore-private-key ./key.private registry.gitlab.com/<namespace>/<repository_name>/<image_name>:latest
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secrets: [sigstore_private_key, registry_login_token]
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```
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