Advertise: UDP Multicast on Linux systems with more NICs: datagrams could be delayed or lost -------------------------------------------------------------------------------------------- Key: MODCLUSTER-487 URL: https://issues.jboss.org/browse/MODCLUSTER-487 Project: mod_cluster Issue Type: Bug Components: Native (httpd modules) Affects Versions: 1.2.11.Final, 1.3.1.Final Environment: Linux, multiple NICs environment Reporter: Michal Karm Babacek Assignee: Michal Karm Babacek Priority: Critical Attachments: advertise-linux3_x86_64.zip, advertise-windows_x86.zip, Advertize.class Credit where it's due: the issue was first spotted by [~rhatlapa]. h3. Problem It appears that trying to send to all interfaces with {{NULL}} or {{"0.0.0.0"}} in the following statement actually picks the first non-loopback interface and sends to it. The result is that there is no datagram on other interfaces. Surprisingly, this is not deterministic though: After dozens or hundreds of messages, eventually one datagram reaches another interface. {code} if ((rv = apr_sockaddr_info_get(&ma_niface_sa, NULL, ma_mgroup_sa->family, 0, APR_UNSPEC, pool)) != APR_SUCCESS) { ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, "mod_advertise: ma_group_join apr_sockaddr_info_get(0.0.0.0:0) failed"); return rv; } {code} h3. Impact Picture this simple scenario: There are two interfaces, e.g. {noformat} enp1s0 10.16.88.187 enp2s0 172.18.0.1 {noformat} listed in this exact order with {{ip addr show}}. One has an EAP 7 (Wildfly 10) instance with mod_cluster bound to {{172.18.0.1}} IP address, which implies {{enp2s0}} interface. Furthermore, one has an Apache HTTP Server instance with mod_cluster bound to {{172.18.0.1}} IP address, i.e. MCMP VirtualHost and main VirtualHost all Listen on this IP address. Result: Without advertising, using an explicit {{proxy-list}}, all is well. MCMP works, requests work, balancing works. On the other hand, relying on advertisement, it could take EAP 7 (Wildfly 10) *minutes* to register with the balancer. The reason is that a vast majority of UDP Multicast datagrams arrives at enp1s0 and EAP 7 (Wildfly 10) doesn't see them. h3. Reproducer Lemme demonstrate with a recently refactored [advertise.c|https://github.com/Karm/mod_cluster/tree/advertise-native-tes...] utility for sending datagrams and the well known [Advertize.java|https://raw.githubusercontent.com/modcluster/mod_cluster/m...] utility for receiving them. Your your convenience, here are binaries built from the aforementioned sources: * Advertize java utility: [^Advertize.class] * advertise native utility (Linux3 x86_64): [^advertise] * advertise native utility (WIndows x86): [^advertise.exe] h3. Demonstration on Linux h4. System {noformat} [mbabacek@perf09 ~]$ ip addr show 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever 2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000 link/ether 00:18:8b:7a:46:04 brd ff:ff:ff:ff:ff:ff inet 10.16.88.187/21 brd 10.16.95.255 scope global enp1s0 valid_lft forever preferred_lft forever inet 10.16.93.253/21 brd 10.16.95.255 scope global secondary enp1s0 valid_lft forever preferred_lft forever 3: enp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000 link/ether 00:18:8b:7a:46:05 brd ff:ff:ff:ff:ff:ff inet 172.17.72.254/19 brd 172.17.95.255 scope global enp2s0 valid_lft forever preferred_lft forever 4: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN link/ether 02:42:07:ab:74:f9 brd ff:ff:ff:ff:ff:ff inet 172.18.0.1/16 scope global docker0 valid_lft forever preferred_lft forever {noformat} h4. Java {noformat} [mbabacek@perf09 ~]$ java -version openjdk version "1.8.0_71" OpenJDK Runtime Environment (build 1.8.0_71-b15) OpenJDK 64-Bit Server VM (build 25.71-b15, mixed mode) {noformat} h4.Advertise SENT {noformat} [mbabacek@perf09 ~]$ date;./advertise -a 224.0.1.102 -p 33364 Mon Mar 21 12:39:51 EDT 2016 UDP Multicast address to send datagrams to. Value: 224.0.1.102 UDP Multicast port. Value: 33364 IP address of the NIC to bound to. Value: NULL apr_socket_bind on 0.0.0.0:0 apr_mcast_join on 0.0.0.0:0 apr_socket_sendto to 224.0.1.102:33364 {noformat} h4. Advertize RECEIVED YES (/) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 Linux like OS ready waiting... received: Advertize !!! Mon, 21 Mar 2016 16:39:51 GMT received from /10.16.88.187:38907 {noformat} YES (/) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 10.16.88.187 Linux like OS ready waiting... received: Advertize !!! Mon, 21 Mar 2016 16:39:51 GMT received from /10.16.88.187:38907 {noformat} NO (x) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 172.17.72.254 Linux like OS ready waiting... {noformat} YES (/) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 0.0.0.0 Linux like OS ready waiting... received: Advertize !!! Mon, 21 Mar 2016 16:39:51 GMT received from /10.16.88.187:38907 {noformat} And now let's take a look at {{172.17.72.254}}, i.e. {{enp2s0}} h4. Advertise SENT {noformat} [mbabacek@perf09 ~]$ date;./advertise -a 224.0.1.102 -p 33364 -n 172.17.72.254 Mon Mar 21 12:42:57 EDT 2016 UDP Multicast address to send datagrams to. Value: 224.0.1.102 UDP Multicast port. Value: 33364 IP address of the NIC to bound to. Value: 172.17.72.254 apr_socket_bind on 172.17.72.254:0 apr_mcast_join on 172.17.72.254:0 apr_socket_sendto to 224.0.1.102:33364 {noformat} h4. Advertize RECEIVED NO (x) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 Linux like OS ready waiting... {noformat} NO (x) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 10.16.88.187 Linux like OS ready waiting... {noformat} YES (/) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 172.17.72.254 Linux like OS ready waiting... received: Advertize !!! Mon, 21 Mar 2016 16:42:57 GMT received from /172.17.72.254:35452 {noformat} NO (x) {noformat} [mbabacek@perf09 ~]$ java Advertize 224.0.1.102 33364 0.0.0.0 Linux like OS ready waiting... {noformat} h3. Demonstration on Windows One could note that the problem doesn't exist on Windows. All interfaces receive advertising. h4. Advertise SENT {noformat} C:\Users\karm\advertise-build λ advertise.exe -a 224.0.1.102 -p 33364 UDP Multicast address to send datagrams to. Value: 224.0.1.102 UDP Multicast port. Value: 33364 IP address of the NIC to bound to. Value: NULL apr_socket_bind on 0.0.0.0:0 apr_mcast_join on 0.0.0.0:0 apr_socket_sendto to 224.0.1.102:33364 {noformat} h4. Advertize RECEIVED YES (/) {noformat} C:\Users\karm\WORKSPACE λ "C:\Program Files\Java\jdk1.8.0_74\bin\java" Advertize 224.0.1.102 33364 ready waiting... received: Advertize !!! Mon, 21 Mar 2016 18:07:50 GMT received from /192.168.122.52:61805 {noformat} YES (/) {noformat} C:\Users\karm\WORKSPACE λ "C:\Program Files\Java\jdk1.8.0_74\bin\java" Advertize 224.0.1.102 33364 192.168.122.52 ready waiting... received: Advertize !!! Mon, 21 Mar 2016 18:07:50 GMT received from /192.168.122.52:61805 {noformat} YES (/) {noformat} C:\Users\karm\WORKSPACE λ "C:\Program Files\Java\jdk1.8.0_74\bin\java" Advertize 224.0.1.102 33364 192.168.122.199 ready waiting... received: Advertize !!! Mon, 21 Mar 2016 18:07:50 GMT received from /192.168.122.52:61805 {noformat} h4. Advertise SENT {noformat} C:\Users\karm\advertise-build λ advertise.exe -a 224.0.1.102 -p 33364 -n 192.168.122.199 UDP Multicast address to send datagrams to. Value: 224.0.1.102 UDP Multicast port. Value: 33364 IP address of the NIC to bound to. Value: 192.168.122.199 apr_socket_bind on 192.168.122.199:0 apr_mcast_join on 192.168.122.199:0 apr_socket_sendto to 224.0.1.102:33364 {noformat} h4. Advertize RECEIVED YES (/) {noformat} C:\Users\karm\WORKSPACE λ "C:\Program Files\Java\jdk1.8.0_74\bin\java" Advertize 224.0.1.102 33364 ready waiting... received: Advertize !!! Mon, 21 Mar 2016 18:09:55 GMT received from /192.168.122.199:52781 {noformat} YES (/) {noformat} C:\Users\karm\WORKSPACE λ "C:\Program Files\Java\jdk1.8.0_74\bin\java" Advertize 224.0.1.102 33364 192.168.122.52 ready waiting... received: Advertize !!! Mon, 21 Mar 2016 18:09:55 GMT received from /192.168.122.199:52781 {noformat} YES (/) {noformat} C:\Users\karm\WORKSPACE λ "C:\Program Files\Java\jdk1.8.0_74\bin\java" Advertize 224.0.1.102 33364 192.168.122.199 ready waiting... received: Advertize !!! Mon, 21 Mar 2016 18:09:55 GMT received from /192.168.122.199:52781 {noformat} Ideas? :) [~jfclere], [~rhusar] I suggest adding {{bindaddr}} instead of NULL or perhaps adding a configuration directive that lets one to pick either MCMP VirtualHost ip address or default -- NULL.