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https://issues.apache.org/jira/browse/TS-4570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15357899#comment-15357899
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ASF subversion and git services commented on TS-4570:
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Commit ab84e0eb928207ff4d8cb1c11d54203a6bf157d7 in trafficserver's branch
refs/heads/master from [[email protected]]
[ https://git-wip-us.apache.org/repos/asf?p=trafficserver.git;h=ab84e0e ]
TS-4570: Return to TS_HTTP_OS_DNS_HOOK if server address is set.
Using HostDB, Traffic Server will try to connect to all the resolved
IP addresses if the connection fail. However if a plugin sets the
address using some out-of-band knowledge and TSHttpTxnServerAddrSet,
it onlt gets to set the address once.
This change returns the state machine to the OS_DNS_HOOK API callout
so that the plugin can have an opportunity to set a different server
address.
> Return to TS_HTTP_OS_DNS_HOOK after explicit DNS
> ------------------------------------------------
>
> Key: TS-4570
> URL: https://issues.apache.org/jira/browse/TS-4570
> Project: Traffic Server
> Issue Type: Improvement
> Components: Core, TS API
> Reporter: James Peach
> Fix For: sometime
>
>
> Consider the case of a plugin that has out -of-band routing knowledge
> equivalent to DNS. So for a domain, it might have a number of possible IP
> addresses. Remap plugins can implement {{TSRemapOSResponse}}, which is called
> in the connection result handling path, but there's no facility for global
> plugins to reroute the request.
> In my case, I'm largely doing forward proxying, so I don't have a remap rule
> for everything I need to route. Hence I'm a global plugin.
> Here is a relatively hacky patch that backs the state machine back up to
> {{TS_HTTP_OS_DNS_HOOK}} if we get a connection failure, have retries left,
> and a plugin has called {{TSHttpTxnServerAddrSet}}.
> {code}
> $ git diff proxy/http/HttpTransact.cc
> diff --git a/proxy/http/HttpTransact.cc b/proxy/http/HttpTransact.cc
> index 5ef0430..3363af1 100644
> --- a/proxy/http/HttpTransact.cc
> +++ b/proxy/http/HttpTransact.cc
> @@ -3762,6 +3762,11 @@ HttpTransact::handle_response_from_server(State *s)
> // families - that is locked in by the client source address.
>
> s->state_machine->ua_session->set_host_res_style(ats_host_res_match(&s->current.server->dst_addr.sa));
> TRANSACT_RETURN(SM_ACTION_DNS_LOOKUP, OSDNSLookup);
> + } else if (s->api_server_addr_set) {
> + // If the address was set by a plugin, give it another chance.
> + s->dns_info.os_addr_style = DNSLookupInfo::OS_ADDR_TRY_HOSTDB;
> + s->current.attempts++;
> + TRANSACT_RETURN(SM_ACTION_API_OS_DNS, OSDNSLookup);
> } else if ((s->dns_info.srv_lookup_success ||
> s->host_db_info.is_rr_elt()) &&
> (s->txn_conf->connect_attempts_rr_retries > 0) &&
> (s->current.attempts %
> s->txn_conf->connect_attempts_rr_retries == 0)) {
> {code}
> Note that some plugins might be unprepared for {{TS_HTTP_OS_DNS_HOOK}} to be
> called multiple times, so we should document that.
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