Use lib-common DownwardAPI to retrieve pod IP

This change uses the `lib-common` env `DownwardAPI` [1] to write the pods IP
to the env vars of the pod. We then retrieve this in `local_settings.py` to populate
`ALLOWED_HOSTS`.

[1] https://github.com/openstack-k8s-operators/lib-common/blob/main/modules/common/env/env.go#L100-L114

Fixes #487
Jira: https://issues.redhat.com/browse/OSPRH-19216
Signed-off-by: Brendan Shephard <bshephar@bne-home.net>

Author: bshephar

internal/horizon/deployment.go

@@ -191,6 +191,7 @@ func getEnvVars(configHash string, enabledServices map[string]string) map[string
 	envVars["ENABLE_WATCHER"] = env.SetValue(enabledServices["watcher"])
 	envVars["CONFIG_HASH"] = env.SetValue(configHash)
 	envVars["UNPACK_THEME"] = env.SetValue("true")
+	envVars["POD_IP"] = env.DownwardAPI("status.podIP")
 
 	return envVars
 }

templates/horizon/config/local_settings.py

@@ -56,35 +56,14 @@
 # For more information see:
 # https://docs.djangoproject.com/en/dev/ref/settings/#allowed-hosts
 
-# get_pod_ip retrieves the pod's primary interface IP address. This is necessary
-# due to the dynamic IP addressing of pods. The HealthCheck needs to be able to
-# check the specific pod. We can't simply check via the route, since such a check
-# could land on any of the replicas. Instead, we need to explicity check the pod
-# we're currently running on. Therefore, we need to execute this function to
-# retrieve the IP address, which we will then in turn add to the ALLOWED_HOSTS list.
-def get_pod_ip():
-    import socket
-    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
-    hostport = (
-        "{{ .horizonEndpointHost }}",
-        {{- if .isPublicHTTPS }}
-        443
-        {{- else }}
-        80
-        {{- end }}
-    )
-    try:
-        s.connect(hostport)
-        return s.getsockname()[0]
-    except socket.gaierror:
-        s.close()
-        s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
-        s.connect(hostport)
-        return "[{}]".format(s.getsockname()[0])
-    finally:
-        s.close()
 
-ALLOWED_HOSTS = [get_pod_ip(), "{{ .horizonEndpointHost }}"]
+# Use the environment variable to set pod_ip. We can then use this for
+# ALLOWED_HOSTS to enable liveness and readiness probes.
+pod_ip = os.environ.get('POD_IP', '')
+if pod_ip and ':' in pod_ip:
+    pod_ip = f"[{pod_ip}]"
+
+ALLOWED_HOSTS = [pod_ip, "{{ .horizonEndpointHost }}"] if pod_ip else ["{{ .horizonEndpointHost }}"]
 
 USE_X_FORWARDED_HOST = True