Handle exceptions when cpu_total is zero (#611)

* Handle exceptions when `cpu_total` is zero

* Make sure zero `cpu_total` is handled correctly

* Ensure `system.process.cpu.total.norm.pct` is `0` as well

* Add newline to satisfy the linter

Author: ivasic

elasticapm/metrics/sets/cpu_linux.py

@@ -69,7 +69,10 @@ def before_collect(self):
         with self._read_data_lock:
             prev = self.previous
             delta = {k: new[k] - prev[k] for k in new.keys()}
-            cpu_usage_ratio = delta["cpu_usage"] / delta["cpu_total"]
+            try:
+                cpu_usage_ratio = delta["cpu_usage"] / delta["cpu_total"]
+            except ZeroDivisionError:
+                cpu_usage_ratio = 0
             self.gauge("system.cpu.total.norm.pct").val = cpu_usage_ratio
             # MemAvailable not present in linux before kernel 3.14
             # fallback to MemFree + Buffers + Cache if not present - see #500
@@ -80,7 +83,10 @@ def before_collect(self):
             self.gauge("system.memory.actual.free").val = mem_free
             self.gauge("system.memory.total").val = new["MemTotal"]
 
-            cpu_process_percent = delta["proc_total_time"] / delta["cpu_total"]
+            try:
+                cpu_process_percent = delta["proc_total_time"] / delta["cpu_total"]
+            except ZeroDivisionError:
+                cpu_process_percent = 0
 
             self.gauge("system.process.cpu.total.norm.pct").val = cpu_process_percent
             self.gauge("system.process.memory.size").val = new["vsize"]

tests/metrics/cpu_linux_tests.py

@@ -155,3 +155,28 @@ def test_mem_free_from_memfree_when_memavailable_not_mentioned(tmpdir):
 
     mem_free_expected = sum([359184, 891296, 6416340]) * 1024  # MemFree + Buffers + Cached, in bytes
     assert data["samples"]["system.memory.actual.free"]["value"] == mem_free_expected
+
+
+def test_cpu_usage_when_cpu_total_is_zero(tmpdir):
+    proc_stat_self = os.path.join(tmpdir.strpath, "self-stat")
+    proc_stat = os.path.join(tmpdir.strpath, "stat")
+    proc_meminfo = os.path.join(tmpdir.strpath, "meminfo")
+
+    for path, content in (
+        (proc_stat, TEMPLATE_PROC_STAT_DEBIAN.format(user=0, idle=0)),
+        (proc_stat_self, TEMPLATE_PROC_STAT_SELF.format(utime=0, stime=0)),
+        (proc_meminfo, TEMPLATE_PROC_MEMINFO_NO_MEMAVAILABLE),
+    ):
+        with open(path, mode="w") as f:
+            f.write(content)
+    metricset = CPUMetricSet(
+        MetricsRegistry(0, lambda x: None),
+        sys_stats_file=proc_stat,
+        process_stats_file=proc_stat_self,
+        memory_stats_file=proc_meminfo,
+    )
+    data = next(metricset.collect())
+
+    cpu_total_expected = 0
+    assert data["samples"]["system.cpu.total.norm.pct"]["value"] == cpu_total_expected
+    assert data["samples"]["system.process.cpu.total.norm.pct"]["value"] == cpu_total_expected