mirror of
https://git.deuxfleurs.fr/Deuxfleurs/garage.git
synced 2024-12-01 20:41:01 +00:00
45 lines
2 KiB
Markdown
45 lines
2 KiB
Markdown
|
+++
|
||
|
|
title = "Request routing logic"
|
||
|
|
weight = 10
|
||
|
|
+++
|
||
|
|
|
||
|
|
Data retrieval requests to Garage endpoints (S3 API and websites) are resolved
|
||
|
|
to an individual object in a bucket. Since objects are replicated to multiple nodes
|
||
|
|
Garage must ensure consistency before answering the request.
|
||
|
|
|
||
|
|
## Using quorum to ensure consistency
|
||
|
|
|
||
|
|
Garage ensures consistency by attempting to establish a quorum with the
|
||
|
|
data nodes responsible for the object. When a majority of the data nodes
|
||
|
|
have provided metadata on a object Garage can then answer the request.
|
||
|
|
|
||
|
|
When a request arrives Garage will, assuming the recommended 3 replicas, perform the following actions:
|
||
|
|
|
||
|
|
- Make a request to the two preferred nodes for object metadata
|
||
|
|
- Try the third node if one of the two initial requests fail
|
||
|
|
- Check that the metadata from at least 2 nodes match
|
||
|
|
- Check that the object hasn't been marked deleted
|
||
|
|
- Answer the request with inline data from metadata if object is small enough
|
||
|
|
- Or get data blocks from the preferred nodes and answer using the assembled object
|
||
|
|
|
||
|
|
Garage dynamically determines which nodes to query based on health, preference, and
|
||
|
|
which nodes actually host a given data. Garage has no concept of "primary" so any
|
||
|
|
healthy node with the data can be used as long as a quorum is reached for the metadata.
|
||
|
|
|
||
|
|
## Node health
|
||
|
|
|
||
|
|
Garage keeps a TCP session open to each node in the cluster and periodically pings them. If a connection
|
||
|
|
cannot be established, or a node fails to answer a number of pings, the target node is marked as failed.
|
||
|
|
Failed nodes are not used for quorum or other internal requests.
|
||
|
|
|
||
|
|
## Node preference
|
||
|
|
|
||
|
|
Garage prioritizes which nodes to query according to a few criteria:
|
||
|
|
|
||
|
|
- A node always prefers itself if it can answer the request
|
||
|
|
- Then the node prioritizes nodes in the same zone
|
||
|
|
- Finally the nodes with the lowest latency are prioritized
|
||
|
|
|
||
|
|
|
||
|
|
For further reading on the cluster structure look at the [gateway](@/documentation/cookbook/gateways.md)
|
||
|
|
and [cluster layout management](@/documentation/reference-manual/layout.md) pages.
|