Improve and clean up supervised process support. (#8036)

* Configuration file default should now be "auto".
* Expose "process_supervised" as an info field.
* Log messages improvements (clarify required systemd config, report
  auto-detected supervision mode, etc.)
* Set server.supervised properly, so it can take precedence of
  "daemonize" configuration.
* Produce clear warning if systemd is detected/requested but executable
  is compiled without support for it, instead of silently ignoring.
* Handle systemd notification error on startup, and turn off supervised
  mode if it failed.

2 files changed, 74 insertions, 36 deletions

diff --git a/redis.conf b/redis.conf
index d28c17b64..dcb5f6241 100644
--- a/redis.conf
+++ b/redis.conf
@@ -228,6 +228,7 @@ tcp-keepalive 300
 
 # By default Redis does not run as a daemon. Use 'yes' if you need it.
 # Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
+# When Redis is supervised by upstart or systemd, this parameter has no impact.
 daemonize no
 
 # If you run Redis from upstart or systemd, Redis can interact with your
@@ -236,11 +237,17 @@ daemonize no
 #   supervised upstart - signal upstart by putting Redis into SIGSTOP mode
 #                        requires "expect stop" in your upstart job config
 #   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET
+#                        on startup, and updating Redis status on a regular
+#                        basis.
 #   supervised auto    - detect upstart or systemd method based on
 #                        UPSTART_JOB or NOTIFY_SOCKET environment variables
 # Note: these supervision methods only signal "process is ready."
 #       They do not enable continuous pings back to your supervisor.
-supervised no
+#
+# The default is "no". To run under upstart/systemd, you can simply uncomment
+# the line below:
+#
+# supervised auto
 
 # If a pid file is specified, Redis writes it where specified at startup
 # and removes it at exit.
diff --git a/src/server.c b/src/server.c
index cef9f7185..1ce6b68bd 100644
--- a/src/server.c
+++ b/src/server.c
@@ -4247,11 +4247,20 @@ sds genRedisInfoString(const char *section) {
         static int call_uname = 1;
         static struct utsname name;
         char *mode;
+        char *supervised;
 
         if (server.cluster_enabled) mode = "cluster";
         else if (server.sentinel_mode) mode = "sentinel";
         else mode = "standalone";
 
+        if (server.supervised) {
+            if (server.supervised_mode == SUPERVISED_UPSTART) supervised = "upstart";
+            else if (server.supervised_mode == SUPERVISED_SYSTEMD) supervised = "systemd";
+            else supervised = "unknown";
+        } else {
+            supervised = "no";
+        }
+
         if (sections++) info = sdscat(info,"\r\n");
 
         if (call_uname) {
@@ -4275,6 +4284,7 @@ sds genRedisInfoString(const char *section) {
             "atomicvar_api:%s\r\n"
             "gcc_version:%i.%i.%i\r\n"
             "process_id:%I\r\n"
+            "process_supervised:%s\r\n"
             "run_id:%s\r\n"
             "tcp_port:%i\r\n"
             "uptime_in_seconds:%I\r\n"
@@ -4300,6 +4310,7 @@ sds genRedisInfoString(const char *section) {
             0,0,0,
 #endif
             (int64_t) getpid(),
+            supervised,
             server.runid,
             server.port ? server.port : server.tls_port,
             (int64_t)uptime,
@@ -5224,62 +5235,82 @@ void redisSetCpuAffinity(const char *cpulist) {
 #endif
 }
 
-/*
- * Check whether systemd or upstart have been used to start redis.
- */
+/* Send a notify message to systemd. Returns sd_notify return code which is
+ * a positive number on success. */
+int redisCommunicateSystemd(const char *sd_notify_msg) {
+#ifdef HAVE_LIBSYSTEMD
+    int ret = sd_notify(0, sd_notify_msg);
+
+    if (ret == 0)
+        serverLog(LL_WARNING, "systemd supervision error: NOTIFY_SOCKET not found!");
+    else if (ret < 0)
+        serverLog(LL_WARNING, "systemd supervision error: sd_notify: %d", ret);
+    return ret;
+#else
+    UNUSED(sd_notify_msg);
+    return 0;
+#endif
+}
 
-int redisSupervisedUpstart(void) {
+/* Attempt to set up upstart supervision. Returns 1 if successful. */
+static int redisSupervisedUpstart(void) {
     const char *upstart_job = getenv("UPSTART_JOB");
 
     if (!upstart_job) {
         serverLog(LL_WARNING,
-                "upstart supervision requested, but UPSTART_JOB not found");
+                "upstart supervision requested, but UPSTART_JOB not found!");
         return 0;
     }
 
-    serverLog(LL_NOTICE, "supervised by upstart, will stop to signal readiness");
+    serverLog(LL_NOTICE, "supervised by upstart, will stop to signal readiness.");
     raise(SIGSTOP);
     unsetenv("UPSTART_JOB");
     return 1;
 }
 
-int redisCommunicateSystemd(const char *sd_notify_msg) {
-    const char *notify_socket = getenv("NOTIFY_SOCKET");
-    if (!notify_socket) {
-        serverLog(LL_WARNING,
-                "systemd supervision requested, but NOTIFY_SOCKET not found");
-    }
-
-    #ifdef HAVE_LIBSYSTEMD
-    (void) sd_notify(0, sd_notify_msg);
-    #else
-    UNUSED(sd_notify_msg);
-    #endif
+/* Attempt to set up systemd supervision. Returns 1 if successful. */
+static int redisSupervisedSystemd(void) {
+#ifndef HAVE_LIBSYSTEMD
+    serverLog(LL_WARNING,
+            "systemd supervision requested or auto-detected, but Redis is compiled without libsystemd support!");
     return 0;
+#else
+    if (redisCommunicateSystemd("STATUS=Redis is loading...\n") <= 0)
+        return 0;
+    serverLog(LL_NOTICE,
+        "Supervised by systemd. Please make sure you set appropriate values for TimeoutStartSec and TimeoutStopSec in your service unit.");
+    return 1;
+#endif
 }
 
 int redisIsSupervised(int mode) {
-    if (mode == SUPERVISED_AUTODETECT) {
-        const char *upstart_job = getenv("UPSTART_JOB");
-        const char *notify_socket = getenv("NOTIFY_SOCKET");
+    int ret = 0;
 
-        if (upstart_job) {
-            redisSupervisedUpstart();
-        } else if (notify_socket) {
-            server.supervised_mode = SUPERVISED_SYSTEMD;
-            serverLog(LL_WARNING,
-                "WARNING auto-supervised by systemd - you MUST set appropriate values for TimeoutStartSec and TimeoutStopSec in your service unit.");
-            return redisCommunicateSystemd("STATUS=Redis is loading...\n");
+    if (mode == SUPERVISED_AUTODETECT) {
+        if (getenv("UPSTART_JOB")) {
+            serverLog(LL_VERBOSE, "Upstart supervision detected.");
+            mode = SUPERVISED_UPSTART;
+        } else if (getenv("NOTIFY_SOCKET")) {
+            serverLog(LL_VERBOSE, "Systemd supervision detected.");
+            mode = SUPERVISED_SYSTEMD;
         }
-    } else if (mode == SUPERVISED_UPSTART) {
-        return redisSupervisedUpstart();
-    } else if (mode == SUPERVISED_SYSTEMD) {
-        serverLog(LL_WARNING,
-            "WARNING supervised by systemd - you MUST set appropriate values for TimeoutStartSec and TimeoutStopSec in your service unit.");
-        return redisCommunicateSystemd("STATUS=Redis is loading...\n");
     }
 
-    return 0;
+    switch (mode) {
+        case SUPERVISED_UPSTART:
+            ret = redisSupervisedUpstart();
+            break;
+        case SUPERVISED_SYSTEMD:
+            ret = redisSupervisedSystemd();
+            break;
+        default:
+            break;
+    }
+
+    if (ret)
+        server.supervised_mode = mode;
+
+    return ret;
 }
 
 int iAmMaster(void) {