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plugin/cache: Add refresh mode setting to serve_stale (#5131)

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This PR adds an optional REFRESH_MODE parameter on the serve_stale configuration directive of the
cache plugin, which verifies that the upstream is still unavailable before returning stale entries.

Signed-off-by: Antoine Tollenaere <atollena@gmail.com>
This commit is contained in:
Antoine Tollenaere
2022-05-02 19:16:33 +02:00
committed by GitHub
parent c3572fdb30
commit 66f2ac7568
6 changed files with 170 additions and 25 deletions
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9
plugin/cache/README.md vendored
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@@ -37,7 +37,7 @@ cache [TTL] [ZONES...] {
success CAPACITY [TTL] [MINTTL]
denial CAPACITY [TTL] [MINTTL]
prefetch AMOUNT [[DURATION] [PERCENTAGE%]]
serve_stale [DURATION]
serve_stale [DURATION] [REFRESH_MODE]
}
~~~
@@ -57,7 +57,12 @@ cache [TTL] [ZONES...] {
* `serve_stale`, when serve\_stale is set, cache always will serve an expired entry to a client if there is one
available. When this happens, cache will attempt to refresh the cache entry after sending the expired cache
entry to the client. The responses have a TTL of 0. **DURATION** is how far back to consider
stale responses as fresh. The default duration is 1h.
stale responses as fresh. The default duration is 1h. **REFRESH_MODE** controls when the attempt to refresh
the cache happens. `verified` will first verify that an entry is still unavailable from the source before sending
the stale response to the client. `immediate` will immediately send the expired response to the client before
checking to see if the entry is available from the source. **REFRESH_MODE** defaults to `immediate`. Setting this
value to `verified` can lead to increased latency when serving stale responses, but will prevent stale entries
from ever being served if an updated response can be retrieved from the source.
## Capacity and Eviction