Add cache for CNAME mappings resolved during lookup of DNS entries.#8314
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normanmaurer merged 2 commits into4.1from Sep 27, 2018
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Add cache for CNAME mappings resolved during lookup of DNS entries.#8314normanmaurer merged 2 commits into4.1from
normanmaurer merged 2 commits into4.1from
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Also /cc @slandelle @vietj |
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Motivation: If the CNAMEd hostname is backed by load balancing component, typically the final A or AAAA DNS records have small TTL. However, the CNAME record itself is setup with longer TTL. For example: * x.netty.io could be CNAMEd to y.netty.io with TTL of 5 min * A / AAAA records for y.netty.io has a TTL of 0.5 min In current Netty implementation, original hostname is saved in resolved cached with the TTL of final A / AAAA records. When that cache entry expires, Netty recursive resolver sends at least two queries — 1st one to be resolved as CNAME record and the 2nd one to resolve the hostname in CNAME record. If CNAME record was cached, only the 2nd query would be needed most of the time. 1st query would be needed less frequently. Modifications: Add a new CnameCache that will be used to cache CNAMEs and so may reduce queries. Result: Less queries needed when CNAME is used.
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trustin
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Sep 27, 2018
| * A cache for {@code CNAME}s. | ||
| */ | ||
| @UnstableApi | ||
| public interface CnameCache { |
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DnsCnameCache? Not strong on this though.
| } | ||
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| /** | ||
| * Returns the cname cache. |
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- cname cache ->
{@link CnameCache}?
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@trustin addressed. |
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normanmaurer
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Motivation: In netty there is a seperate CNAME cache that is used to cache CNAMEs that are resolved during resolving an A / AAAA record. While this sounded like a great idea when I first implemented this in netty it turned out this is problematic and may produce errors while resolving hostnames later on. The problem with the CNAME cache is that we may end up with entries in the CNAME cache wile the original cached resolution was already removed from the cache (due TTL). In this case we may find an entry in teh CNAME cache that we will then try to resolve via the specified nameserver. This resolution may fail as the nameserver may not return an entry for the previous cached CNAME. This usually happens when we receive the full "resolution chain" during query for an A / AAAA record. This problem was introduced by #8314 Modifications: - Use the NoopDnsCnameCache by default - Deprecate methods that allow to set a custom DnsCnameCache - Deprecate DnsCnameCache and all the implementations - Add unit test Result: Fixes resolution problem caused by cached cname records
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Motivation:
If the CNAMEd hostname is backed by load balancing component, typically the final A or AAAA DNS records have small TTL. However, the CNAME record itself is setup with longer TTL.
For example:
In current Netty implementation, original hostname is saved in resolved cached with the TTL of final A / AAAA records. When that cache entry expires, Netty recursive resolver sends at least two queries — 1st one to be resolved as CNAME record and the 2nd one to resolve the hostname in CNAME record.
If CNAME record was cached, only the 2nd query would be needed most of the time. 1st query would be needed less frequently.
Modifications:
Add a new CnameCache that will be used to cache CNAMEs and so may reduce queries.
Result:
Less queries needed when CNAME is used.