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https://issues.apache.org/jira/browse/TS-4468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15312663#comment-15312663
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Jered Floyd commented on TS-4468:
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I would argue that the default must be "safe" as in unlikely to cause error. I
also agree that session reuse is valuable.
Therefore, I suggest that the default behavior is either:
1) "host" (or "both") matching compares _target_ hostname instead of
_replacement_ FQDN, or
2) "host" (or "both") matching compares target hostname in addition to
replacement FQDN.
I think option 1 there is simpler and sufficient, but please sanity check that.
This solution would fix the problem and retain all the benefits of session
reuse.
I do not see any value in adding an further matrix of options that includes
target hostname for server_session_sharing.match -- target hostname should
either replace or augment replacement FQDN.
There is also the third option you identified, 3) Don't set SNI name on origin
connections. I think this is undesirable as it is a functional regression.
> http.server_session_sharing.match = both unsafe with HTTPS
> ----------------------------------------------------------
>
> Key: TS-4468
> URL: https://issues.apache.org/jira/browse/TS-4468
> Project: Traffic Server
> Issue Type: Bug
> Components: HTTP, SSL
> Affects Versions: 6.1.1
> Reporter: Jered Floyd
> Fix For: 7.0.0
>
>
> proxy.config.http.server_session_sharing.match has a default value of "both",
> which compares IP address, port, and FQDN when determining whether a
> connection can be reused for further user agent requests.
> The "host" (FQDN) matching does not behave safely when ATS is operating as a
> reverse proxy. The compared value is the origin server FQDN after mapping,
> rather than the initial "Host" target.
> If multiple Hosts map to the same origin server and the scheme is HTTPS, ATS
> will attempt to reuse a connection that may have an SNI Host that does not
> match the HTTP Host. With Apache 2.4 origin servers this results in 400 Bad
> Request to the user agent.
> PROBLEM REPRODUCTION:
> You can observe this behavior with two mapping rules such as:
> map https://example.com/ https://origin.example.com/
> map https://www.example.com/ https://origin.example.com/
> Non-caching clients alternately fetching URIs from the two targets will see
> 400 Bad Request responses intermittently.
> WORKAROUND:
> proxy.config.http.server_session_sharing.match should have a default value of
> "none" when proxy.config.reverse_proxy.enabled is "1"
> SUGGESTED FIXES:
> In order of completeness:
> 1) Do not share server sessions on reverse_proxy requests.
> 2) Do not share server sessions on reverse_proxy requests where scheme is
> HTTPS.
> 3) Compare target host (SNI host) rather than replacement host when
> determining if reuse of server session is allowed (when
> server_session_sharing.match is set to "host" or "both").
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