Guard registration of process-wide metrics by existence of the requisite /proc entries

synapse/metrics/__init__.py

@@ -115,6 +115,10 @@ def render_all():
 TICKS_PER_SEC = 100
 BYTES_PER_PAGE = 4096
 
+HAVE_PROC_STAT = os.path.exists("/proc/stat")
+HAVE_PROC_SELF_STAT = os.path.exists("/proc/self/stat")
+HAVE_PROC_SELF_LIMITS = os.path.exists("/proc/self/limits")
+
 rusage = None
 stats = None
 fd_counts = None
@@ -122,13 +126,11 @@ fd_counts = None
 # In order to report process_start_time_seconds we need to know the machine's
 # boot time, because the value in /proc/self/stat is relative to this
 boot_time = None
-try:
+if HAVE_PROC_STAT:
     with open("/proc/stat") as _procstat:
         for line in _procstat:
             if line.startswith("btime "):
                 boot_time = int(line.split()[1])
-except IOError:
-    pass
 
 TYPES = {
     stat.S_IFSOCK: "SOCK",
@@ -144,6 +146,7 @@ def update_resource_metrics():
     global rusage
     rusage = getrusage(RUSAGE_SELF)
 
+    if HAVE_PROC_SELF_STAT:
         global stats
         with open("/proc/self/stat") as s:
             line = s.read()
@@ -195,6 +198,7 @@ get_metrics_for("process").register_callback("fds", _process_fds, labels=["type"
 ## New prometheus-standard metric names
 process_metrics = get_metrics_for("process");
 
+if HAVE_PROC_SELF_STAT:
     process_metrics.register_callback(
         "cpu_user_seconds_total", lambda: float(stats[11]) / TICKS_PER_SEC
     )
@@ -216,6 +220,11 @@ process_metrics.register_callback(
         "open_fds", lambda: sum(fd_counts.values())
     )
 
+    process_metrics.register_callback(
+        "start_time_seconds", lambda: boot_time + int(stats[19]) / TICKS_PER_SEC
+    )
+
+if HAVE_PROC_SELF_LIMITS:
     def _get_max_fds():
         with open("/proc/self/limits") as limits:
             for line in limits:
@@ -229,10 +238,6 @@ process_metrics.register_callback(
         "max_fds", lambda: _get_max_fds()
     )
 
-process_metrics.register_callback(
-    "start_time_seconds", lambda: boot_time + int(stats[19]) / TICKS_PER_SEC
-)
-
 reactor_metrics = get_metrics_for("reactor")
 tick_time = reactor_metrics.register_distribution("tick_time")
 pending_calls_metric = reactor_metrics.register_distribution("pending_calls")