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https://issues.apache.org/jira/browse/TS-4570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15356226#comment-15356226
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ASF GitHub Bot commented on TS-4570:
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Github user jpeach commented on the issue:
https://github.com/apache/trafficserver/pull/740
@SolidWallOfCode I filed
[TS-4574](https://issues.apache.org/jira/browse/TS-4574) to clear the explicit
address. However now that I know a bit more about how the DNS resolutions
works, the patch there is not really sufficient.
FWIW my current code samples the first DNS address before setting any
addresses and restores that if all else fails. For now I'm giving up DNS RR.
> 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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