[bgpd]: Check zebra is ready to connect when starting bgpd (#6478)

Fix #5026

There is a race condition between zebra server accepts connections and bgpd tries to connect. Bgpd has a chance to try to connect before zebra is ready. In this scenario, bgpd will try again after 10 seconds and operate as normal within these 10 seconds. As a consequence, whatever bgpd tries to sent to zebra will be missing in the 10 seconds. To avoid such a scenario, bgpd should start after zebra is ready to accept connections.

dockers/docker-fpm-frr/Dockerfile.j2

@@ -55,6 +55,7 @@ COPY ["TSB", "/usr/bin/TSB"]
 COPY ["TSC", "/usr/bin/TSC"]
 COPY ["files/supervisor-proc-exit-listener", "/usr/bin"]
 COPY ["critical_processes", "/etc/supervisor"]
+COPY ["bgpd.sh", "/usr/bin/"]
 RUN chmod a+x /usr/bin/TSA && \
     chmod a+x /usr/bin/TSB && \
     chmod a+x /usr/bin/TSC

dockers/docker-fpm-frr/bgpd.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+addr="127.0.0.1"
+port=2601
+
+function help()
+{
+    echo "This script aims to ensure zebra is ready to accept connections before starting bgpd"
+    echo "Usage: $0 [options] [bgpd options]"
+    echo "Options:"
+    echo " -a   Zebra address"
+    echo " -o   Zebra port"
+    exit 1
+}
+
+while getopts ":a:o:h" opt; do
+    case "${opt}" in
+        h) help
+            ;;
+        a) addr=${OPTARG}
+            ;;
+        o) port=${OPTARG}
+            ;;
+    esac
+done
+shift $((OPTIND-1))
+
+timeout 5s bash -c -- "until </dev/tcp/${addr}/${port}; do sleep 0.1;done"
+if [ "$?" != "0" ]; then
+    logger -p error "Error: zebra is not ready to accept connections"
+fi
+
+exec /usr/lib/frr/bgpd "$@"

dockers/docker-fpm-frr/frr/supervisord/supervisord.conf.j2

@@ -51,7 +51,7 @@ dependent_startup=true
 dependent_startup_wait_for=zebra:running
 
 [program:bgpd]
-command=/usr/lib/frr/bgpd -A 127.0.0.1 -M snmp
+command=/usr/bin/bgpd.sh -A 127.0.0.1 -M snmp
 priority=5
 stopsignal=KILL
 autostart=false