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Fix race condition in DNS when using cache (#5398) 

* Fix race condition in DNS when using cache

The healty node filtering was modifying the result from the cache, which
caused a crash when multiple queries were made to the same service
simultaneously.
We now copy the node slice before filtering to ensure we do not modify
the data stored in the cache.

* Fix wording in dns cache config doc

s/dns_max_age/cache_max_age/
This commit is contained in:
Aestek 2019-03-04 15:22:01 +01:00 committed by Matt Keeler
parent 9a7d57d995
commit ce447e0e16
2 changed files with 5 additions and 2 deletions
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5
agent/dns.go
View File

@ -1100,7 +1100,10 @@ func (d *DNSServer) lookupServiceNodes(datacenter, service, tag string, connect
} }
// Filter out any service nodes due to health checks // Filter out any service nodes due to health checks
out.Nodes = out.Nodes.Filter(d.config.OnlyPassing) // We copy the slice to avoid modifying the result if it comes from the cache
nodes := make(structs.CheckServiceNodes, len(out.Nodes))
copy(nodes, out.Nodes)
out.Nodes = nodes.Filter(d.config.OnlyPassing)
return out, nil return out, nil
} }

2
website/source/docs/agent/options.html.md
View File

@ -1078,7 +1078,7 @@ default will automatically work with some tooling.
* <a name="dns_use_cache"></a><a href="dns_use_cache">`use_cache`</a> - When set to true, DNS resolution will use the agent cache described * <a name="dns_use_cache"></a><a href="dns_use_cache">`use_cache`</a> - When set to true, DNS resolution will use the agent cache described
in [agent caching](/api/index.html#agent-caching). This setting affects all service and prepared queries DNS requests. Implies [`allow_stale`](#allow_stale) in [agent caching](/api/index.html#agent-caching). This setting affects all service and prepared queries DNS requests. Implies [`allow_stale`](#allow_stale)
* <a name="dns_cache_max_age"></a><a href="dns_cache_max_age">`dns_max_age`</a> - When [use_cache](#dns_use_cache) is enabled, the agent * <a name="dns_cache_max_age"></a><a href="dns_cache_max_age">`cache_max_age`</a> - When [use_cache](#dns_use_cache) is enabled, the agent
will attempt to re-fetch the result from the servers if the cached value is older than this duration. See: [agent caching](/api/index.html#agent-caching). will attempt to re-fetch the result from the servers if the cached value is older than this duration. See: [agent caching](/api/index.html#agent-caching).
* <a name="domain"></a><a href="#domain">`domain`</a> Equivalent to the * <a name="domain"></a><a href="#domain">`domain`</a> Equivalent to the