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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
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GPG key ID: 4AEE18F83AFDEB23
6 changed files with 170 additions and 25 deletions
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24
plugin/cache/handler.go vendored
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@ -35,19 +35,29 @@ func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
ttl := 0
i := c.getIgnoreTTL(now, state, server)
if i != nil {
ttl = i.ttl(now)
}
if i == nil {
crr := &ResponseWriter{ResponseWriter: w, Cache: c, state: state, server: server, do: do}
return c.doRefresh(ctx, state, crr)
}
ttl = i.ttl(now)
if ttl < 0 {
servedStale.WithLabelValues(server, c.zonesMetricLabel).Inc()
// serve stale behavior
if c.verifyStale {
crr := &ResponseWriter{ResponseWriter: w, Cache: c, state: state, server: server, do: do}
cw := newVerifyStaleResponseWriter(crr)
ret, err := c.doRefresh(ctx, state, cw)
if cw.refreshed {
return ret, err
}
}
// Adjust the time to get a 0 TTL in the reply built from a stale item.
now = now.Add(time.Duration(ttl) * time.Second)
cw := newPrefetchResponseWriter(server, state, c)
go c.doPrefetch(ctx, state, cw, i, now)
if !c.verifyStale {
cw := newPrefetchResponseWriter(server, state, c)
go c.doPrefetch(ctx, state, cw, i, now)
}
servedStale.WithLabelValues(server, c.zonesMetricLabel).Inc()
} else if c.shouldPrefetch(i, now) {
cw := newPrefetchResponseWriter(server, state, c)
go c.doPrefetch(ctx, state, cw, i, now)
@ -70,7 +80,7 @@ func (c *Cache) doPrefetch(ctx context.Context, state request.Request, cw *Respo
}
}
func (c *Cache) doRefresh(ctx context.Context, state request.Request, cw *ResponseWriter) (int, error) {
func (c *Cache) doRefresh(ctx context.Context, state request.Request, cw dns.ResponseWriter) (int, error) {
if !state.Do() {
setDo(state.Req)
}