Emulate behaviour of haproxy-systemd-wrapper.

For reference, see:
http://git.haproxy.org/?p=haproxy.git;a=blob;f=src/haproxy-systemd-wrapper.c;h=f6a9c852b277b5f193d6a952119a149b4cfe3e8b;hb=HEAD

haproxy_wrapper.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+import os
+import sys
+import time
+
+
+def create_haproxy_pipe():
+    pipefd = os.pipe()
+    return pipefd
+
+
+def close_and_swallow(fd):
+    try:
+        os.close(fd)
+    except OSError:
+        # swallow
+        pass
+
+
+def wait_on_haproxy_pipe(pipefd):
+    try:
+        ret = os.read(pipefd[0], 1)
+        if len(ret) == 0:
+            close_and_swallow(pipefd[0])
+            close_and_swallow(pipefd[1])
+            return False
+    except OSError as e:
+        if e.args[0] != errno.EINTR:
+            close_and_swallow(pipefd[0])
+            close_and_swallow(pipefd[1])
+            return False
+    return True
+
+pipefd = create_haproxy_pipe()
+
+pid = os.fork()
+
+if not pid:
+    os.environ["HAPROXY_WRAPPER_FD"] = str(pipefd[1])
+    # Close the read side
+    os.close(pipefd[0])
+    os.execv(sys.argv[1], sys.argv[1:])
+
+# Close the write side
+os.close(pipefd[1])
+while wait_on_haproxy_pipe(pipefd):
+    time.sleep(0.01)

service/haproxy/run

@@ -33,7 +33,7 @@ reload() {
 
     # Trigger reload
     LATEST_HAPROXY_PID=$(cat $PIDFILE)
-    haproxy -p $PIDFILE -f /marathon-lb/haproxy.cfg -D -sf $LATEST_HAPROXY_PID 200>&-
+    /marathon-lb/haproxy_wrapper.py `which haproxy` -p $PIDFILE -f /marathon-lb/haproxy.cfg -D -sf $LATEST_HAPROXY_PID 200>&-
     if [ -n "${HAPROXY_RELOAD_SIGTERM_DELAY-}" ]; then
       sleep $HAPROXY_RELOAD_SIGTERM_DELAY && kill $LATEST_HAPROXY_PID 200>&- 2>/dev/null &
     fi