Emulate behaviour of haproxy-systemd-wrapper. (#390)

This also drops the `HAPROXY_RELOAD_SIGTERM_DELAY` param.

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

Dockerfile

@@ -20,7 +20,7 @@ RUN set -x \
     && export GNUPGHOME="$(mktemp -d)" \
     && gpg --keyserver ha.pool.sks-keyservers.net --recv-keys "$TINI_GPG_KEY" \
     && gpg --batch --verify tini.asc tini \
-    && rm -r "$GNUPGHOME" tini.asc \
+    && rm -rf "$GNUPGHOME" tini.asc \
     && mv tini /usr/bin/tini \
     && chmod +x /usr/bin/tini \
     && tini -- true \

README.md

@@ -278,7 +278,6 @@ The default value when not specified is `redispatch,http-server-close,dontlognul
   < HTTP/1.1 200 OK
   ```
  * Some of the features of marathon-lb assume that it is the only instance of itself running in a PID namespace. i.e. marathon-lb assumes that it is running in a container. Certain features like the `/_mlb_signal` endpoints and the `/_haproxy_getpids` endpoint (and by extension, zero-downtime deployments) may behave unexpectedly if more than one instance of marathon-lb is running in the same PID namespace or if there are other HAProxy processes in the same PID namespace.
- * You may want to set the `HAPROXY_RELOAD_SIGTERM_DELAY` environment variable to a value such as `5m`. This value is passed directly to the `sleep` command, which is executed after every HAProxy reload before sending a SIGTERM to the old HAProxy PIDs (see [service/haproxy/run](service/haproxy/run)). For cases where you expect long-lived TCP connections, you may _not_ want to terminate HAProxy before all connections finish. See [this discussion](http://www.serverphorums.com/read.php?10,862139) for more on HAProxy reloads, and issues [#5](https://github.com/mesosphere/marathon-lb/issues/5), [#71](https://github.com/mesosphere/marathon-lb/issues/71), [#267](https://github.com/mesosphere/marathon-lb/issues/267), [#276](https://github.com/mesosphere/marathon-lb/issues/276), and [#318](https://github.com/mesosphere/marathon-lb/issues/318) for more. If you are reloading so frequently that PIDs are being reused within the delay you specify, this may result in SIGTERMs being sent to the wrong PIDs.
 
 ## Zero-downtime Deployments
 

haproxy_wrapper.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+import os
+import sys
+import time
+import errno
+
+
+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])
+    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(0.005)
+sys.exit(0)

run

@@ -16,11 +16,6 @@ else
   exit 1
 fi
 
-if [ -n "${HAPROXY_RELOAD_SIGTERM_DELAY-}" ]; then
-  echo $HAPROXY_RELOAD_SIGTERM_DELAY > $HAPROXY_SERVICE/env/HAPROXY_RELOAD_SIGTERM_DELAY
-fi
-
-
 # Find the --ssl-certs arg if one was provided,
 # get the certs and remove them and the arg from the list
 # of positional parameters so we don't duplicate them

service/haproxy/run

@@ -33,9 +33,10 @@ reload() {
 
     # Trigger reload
     LATEST_HAPROXY_PID=$(cat $PIDFILE)
-    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 &
+    /marathon-lb/haproxy_wrapper.py `which haproxy` -p $PIDFILE -f /marathon-lb/haproxy.cfg -sf $LATEST_HAPROXY_PID 200>&-
+    local exit_code=$?
+    if [ $exit_code -ne 0 ]; then
+      echo "HAProxy reload failed" 1>&2
     fi
 
     # Remove the firewall rules