Improve systemd integration

Hopefully this patch will fix all systemd-related problems:
- Proxy shell process (which converts signals to `rabbitmqtl stop`) will
  no longer be started under systemd. There is no need in it, as systemd
  unit already contains instructions for graceful shutdown.
- Ready notification for systemd will be sent with the help of `socat`,
  as `systemd-notify` is currently broken for non-root users. `socat` is
  the most lightweight way to do it (other options are using NIF or some
  external helper in Perl).
- epmd will not be able to interfere by sending it's own ready
  notifications.
- systemd journal will contain some additional messages about startup
  and shutdown sequence, just to be sure that everything is working
  correctly.

Fixes #664

1 files changed, 21 insertions, 5 deletions

diff --git a/scripts/rabbitmq-server b/scripts/rabbitmq-server
index a517cc8182..5acc86682b 100755
--- a/scripts/rabbitmq-server
+++ b/scripts/rabbitmq-server
@@ -47,7 +47,7 @@ case "$(uname -s)" in
                    exit $EX_CANTCREAT
                fi
                if ! echo $$ > ${RABBITMQ_PID_FILE}; then
-                   # Bettern diagnostics - otherwise the only report in logs is about failed 'echo'
+                   # Better diagnostics - otherwise the only report in logs is about failed 'echo'
                    # command, but without any other details: neither what script has failed nor what
                    # file output was redirected to.
                    echo "Failed to write pid file: ${RABBITMQ_PID_FILE}"
@@ -58,8 +58,13 @@ esac
 
 RABBITMQ_EBIN_ROOT="${RABBITMQ_HOME}/ebin"
 
+[ "$NOTIFY_SOCKET" ] && RUNNING_UNDER_SYSTEMD=true
+
 set +e
 
+# NOTIFY_SOCKET is needed here to prevent epmd from impersonating the
+# success of our startup sequence to systemd.
+NOTIFY_SOCKET= \
 RABBITMQ_CONFIG_FILE=$RABBITMQ_CONFIG_FILE \
 RABBITMQ_DIST_PORT=$RABBITMQ_DIST_PORT \
     ${ERL_DIR}erl -pa "$RABBITMQ_EBIN_ROOT" \
@@ -172,7 +177,20 @@ check_not_empty() {
     fi
 }
 
-if [ 'x' = "x$RABBITMQ_ALLOW_INPUT" -a -z "$detached" ]; then
+if [ "$RABBITMQ_ALLOW_INPUT" -o "$RUNNING_UNDER_SYSTEMD" -o "$detached" ]; then
+    # Run erlang VM directly, completely replacing current shell
+    # process - so the pid file written in the code above will be
+    # valid (unless detached, which is also handled in the code
+    # above).
+    #
+    # And also this is the correct mode to run the broker under
+    # systemd - there is no need in a proxy process that converts
+    # signals to graceful shutdown command, the unit file should already
+    # contain instructions for graceful shutdown. Also by removing
+    # this additional process we could simply use value returned by
+    # `os:getpid/0` for a systemd ready notification.
+    start_rabbitmq_server "$@"
+else
     # When RabbitMQ runs in the foreground but the Erlang shell is
     # disabled, we setup signal handlers to stop RabbitMQ properly. This
     # is at least useful in the case of Docker.
@@ -181,7 +199,7 @@ if [ 'x' = "x$RABBITMQ_ALLOW_INPUT" -a -z "$detached" ]; then
     RABBITMQ_SERVER_START_ARGS="${RABBITMQ_SERVER_START_ARGS} +B i"
 
     # Signal handlers. They all stop RabbitMQ properly (using
-    # rabbitmqctl stop). Depending on the signal, this script will exwit
+    # rabbitmqctl stop). Depending on the signal, this script will exit
     # with a non-zero error code:
     #   SIGHUP SIGTERM SIGTSTP
     #     They are considered a normal process termination, so the script
@@ -197,6 +215,4 @@ if [ 'x' = "x$RABBITMQ_ALLOW_INPUT" -a -z "$detached" ]; then
     # Block until RabbitMQ exits or a signal is caught.
     # Waits for last command (which is start_rabbitmq_server)
     wait $!
-else
-    start_rabbitmq_server "$@"
 fi