IMHO the current behaviour of mod_proxy_ajp is not correct if a CPING/CPONG fails on a backend connection. In this case the status is set to HTTP_SERVICE_UNAVAILABLE and the scheme handler returns. In the case of an unbalanced backend this results in a HTTP_SERVICE_UNAVAILABLE (503) to be returned to the client. But a failing CPING/CPONG can be caused by a faulty AJP connection that was closed by the backend or a race condition in sending the CPING and closing the connection on the backend. So after the first failed CPING/CPONG we should try again with a new TCP connection and should only return HTTP_SERVICE_UNAVAILABLE if this fails as well. The following (and attached patch) does exactly that. Thoughs to the above and/or to the patch before I commit?
Index: modules/proxy/mod_proxy_ajp.c =================================================================== --- modules/proxy/mod_proxy_ajp.c (revision 692409) +++ modules/proxy/mod_proxy_ajp.c (working copy) @@ -554,6 +554,7 @@ conn_rec *origin = NULL; proxy_conn_rec *backend = NULL; const char *scheme = "AJP"; + int retry; proxy_dir_conf *dconf = ap_get_module_config(r->per_dir_config, &proxy_module); @@ -597,43 +598,53 @@ backend->is_ssl = 0; backend->close = 0; - /* Step One: Determine Who To Connect To */ - status = ap_proxy_determine_connection(p, r, conf, worker, backend, - uri, &url, proxyname, proxyport, - server_portstr, - sizeof(server_portstr)); + retry = 0; + while (retry < 2) { + /* Step One: Determine Who To Connect To */ + status = ap_proxy_determine_connection(p, r, conf, worker, backend, + uri, &url, proxyname, proxyport, + server_portstr, + sizeof(server_portstr)); - if (status != OK) - goto cleanup; + if (status != OK) + break; - /* Step Two: Make the Connection */ - if (ap_proxy_connect_backend(scheme, backend, worker, r->server)) { - ap_log_error(APLOG_MARK, APLOG_ERR, 0, r->server, - "proxy: AJP: failed to make connection to backend: %s", - backend->hostname); - status = HTTP_SERVICE_UNAVAILABLE; - goto cleanup; - } - - /* Handle CPING/CPONG */ - if (worker->ping_timeout_set) { - status = ajp_handle_cping_cpong(backend->sock, r, - worker->ping_timeout); - if (status != APR_SUCCESS) { - backend->close++; - ap_log_error(APLOG_MARK, APLOG_ERR, status, r->server, - "proxy: AJP: cping/cpong failed to %pI (%s)", - worker->cp->addr, - worker->hostname); + /* Step Two: Make the Connection */ + if (ap_proxy_connect_backend(scheme, backend, worker, r->server)) { + ap_log_error(APLOG_MARK, APLOG_ERR, 0, r->server, + "proxy: AJP: failed to make connection to backend: %s", + backend->hostname); status = HTTP_SERVICE_UNAVAILABLE; - goto cleanup; + break; } + + /* Handle CPING/CPONG */ + if (worker->ping_timeout_set) { + status = ajp_handle_cping_cpong(backend->sock, r, + worker->ping_timeout); + /* + * In case the CPING / CPONG failed for the first time we might be + * just out of luck and got a faulty backend connection, but the + * backend might be healthy nevertheless. So ensure that the backend + * TCP connection gets closed and try it once again. + */ + if (status != APR_SUCCESS) { + backend->close++; + ap_log_error(APLOG_MARK, APLOG_ERR, status, r->server, + "proxy: AJP: cping/cpong failed to %pI (%s)", + worker->cp->addr, + worker->hostname); + status = HTTP_SERVICE_UNAVAILABLE; + retry++; + continue; + } + } + /* Step Three: Process the Request */ + status = ap_proxy_ajp_request(p, r, backend, origin, dconf, uri, url, + server_portstr); + break; } - /* Step Three: Process the Request */ - status = ap_proxy_ajp_request(p, r, backend, origin, dconf, uri, url, - server_portstr); -cleanup: /* Do not close the socket */ ap_proxy_release_connection(scheme, backend, r->server); return status; Regards Rüdiger
cping_cpong_retry.diff
Description: cping_cpong_retry.diff