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https://issues.apache.org/jira/browse/TS-4403?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15303027#comment-15303027
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ASF subversion and git services commented on TS-4403:
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Commit 5712179404e1bace464d44d51b277dde684ee5b6 in trafficserver's branch
refs/heads/6.1.x from [~jacksontj]
[ https://git-wip-us.apache.org/repos/asf?p=trafficserver.git;h=5712179 ]
TS-4403: Fix stale-while-revalidate on DNS lookup failures (#609)
HostDB's "stale-while-revalidate" feature allows hostdb to return stale records
while doing the DNS lookup in the background. This works properly in the case
where the resolver goes away, but in the case that an error was returned from
the resolver the record in cache was thrown away. This means that a transient
error out in the DNS infrastructure would cause ATS to drop its stale record it
would have contently served-- this patch simply makes hostdb honor its
stale-while-revalidate contract (if configured). So, in the event that the DNS
result comes back as `failed` hostdb will keep the old one if it is okay with
being served stale.
This closes #609
(cherry picked from commit 131875cbe7b0975c8c3c4f3d20aa55a5c7caba86)
> HostDB's "stale while revalidate" doesn't span failed DNS lookups
> -----------------------------------------------------------------
>
> Key: TS-4403
> URL: https://issues.apache.org/jira/browse/TS-4403
> Project: Traffic Server
> Issue Type: Bug
> Reporter: Thomas Jackson
> Labels: review
> Fix For: 6.1.2, 6.2.0, 7.0.0
>
>
> Right now if you set stale_while_revalidate hostdb will return the stale
> record while waiting on the DNS lookup. In the event that you have the DNS
> timeout set low (lets say 1 second) and the DNS server times out (lets say
> due to an outage of your resolver) then ATS will start replacing all of your
> stale entries (which were working) with error timeout entries (which are
> empty)-- which is bad.
> The stale while revalidate configuration should serve stale records until a
> valid response from DNS comes back-- the patch here should be relatively
> simple, just a bit of a nuisance to test since DNS requires port 53 ;)
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