fix pod ID for kubernetes when using the systemd cgroup driver (#631)

When the systemd cgroup driver is used, cgroup paths will have hyphens (e.g. in pod UIDs)
escaped to underscores. When we're parsing cgroups, we must therefore unescape them.

refs elastic/apm#165

Author: beniwohli

CHANGELOG.md

@@ -7,6 +7,7 @@
 
  * ensure that metrics with value 0 are not collected if they have the `reset_on_collect` flag set (#615)
  * unwrap postgres cursor for newly introduced psycopg2 extensions (#621)
+ * fix pod ID for kubernetes when using the systemd cgroup driver (#631)
 
 ## v5.2.2
 [Check the diff](https://github.com/elastic/apm-agent-python/compare/v5.2.1...v5.2.2)

elasticapm/utils/cgroup.py

@@ -100,6 +100,8 @@ def parse_cgroups(filehandle):
             pod_id = kubepods_match.group(1)
             if not pod_id:
                 pod_id = kubepods_match.group(2)
+                if pod_id:
+                    pod_id = pod_id.replace("_", "-")
             return {"container": {"id": container_id}, "kubernetes": {"pod": {"uid": pod_id}}}
         elif container_id_regexp.match(container_id):
             return {"container": {"id": container_id}}

tests/utils/cgroup_tests.py

@@ -56,7 +56,7 @@
             "1:name=systemd:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-pod90d81341_92de_11e7_8cf2_507b9d4141fa.slice/crio-2227daf62df6694645fee5df53c1f91271546a9560e8600a525690ae252b7f63.scope",
             {
                 "container": {"id": "2227daf62df6694645fee5df53c1f91271546a9560e8600a525690ae252b7f63"},
-                "kubernetes": {"pod": {"uid": "90d81341_92de_11e7_8cf2_507b9d4141fa"}},
+                "kubernetes": {"pod": {"uid": "90d81341-92de-11e7-8cf2-507b9d4141fa"}},
             },
         ),
         (