Jered Floyd created TS-4468:
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Summary: http.server_session_sharing.match = both unsafe in
reverse proxy mode
Key: TS-4468
URL: https://issues.apache.org/jira/browse/TS-4468
Project: Traffic Server
Issue Type: Bug
Components: HTTP
Reporter: Jered Floyd
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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