<p>I have custom metrics exported to <code>Google Cloud Monitoring</code> and i want to scale my deployment according to it.</p>

<p>This is my HPA:</p>

<pre><code>apiVersion: autoscaling/v2beta1
kind: HorizontalPodAutoscaler
metadata:
  name: &lt;DEPLOYMENT&gt;-hpa
  namespace: production
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: &lt;DEPLOYMENT&gt;
  minReplicas: 5
  maxReplicas: 100
  metrics:
  - type: External
    external:
      metricName: "custom.googleapis.com|rabbit_mq|test|messages_count"
      metricSelector:
        matchLabels:
          metric.labels.name: production
      targetValue: 1
</code></pre>

<p>When describing the hpa i see:</p>

<pre><code> Warning  FailedComputeMetricsReplicas  4m23s (x12 over 7m23s)  horizontal-pod-autoscaler  Invalid metrics (1 invalid out of 1), last error was: failed to get externa
l metric custom.googleapis.com|rabbit_mq|test|messages_count: unable to get external metric production/custom.googleapis.com|rabbit_mq|test|messages_count/&amp;LabelSelect
or{MatchLabels:map[string]string{metric.labels.name: production,},MatchExpressions:[],}: unable to fetch metrics from external metrics API: the server is currently una
ble to handle the request (get custom.googleapis.com|rabbit_mq|test|messages_count.external.metrics.k8s.io)
  Warning  FailedGetExternalMetric       2m23s (x20 over 7m23s)  horizontal-pod-autoscaler  unable to get external metric production/custom.googleapis.com|rabbit_mq|te
st|messages_count/&amp;LabelSelector{MatchLabels:map[string]string{metric.labels.name: production,},MatchExpressions:[],}: unable to fetch metrics from external metrics AP
I: the server is currently unable to handle the request (get custom.googleapis.com|rabbit_mq|test|messages_count.external.metrics.k8s.io)
</code></pre>

<p>And:</p>

<pre><code>Metrics:                                                                 ( current / target )
  "custom.googleapis.com|rabbit_mq|test|messages_count" (target value):  &lt;unknown&gt; / 1
</code></pre>

<p>Kubernetes is unable to get the metric.</p>

<p>I validated that the metric is available and updated through the Monitoring dashboard.</p>

<p>Cluster nodes has Full Control for Stackdriver Monitoring:
<a href="https://i.stack.imgur.com/Li2HW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Li2HW.png" alt="enter image description here"></a></p>

<p>Kubernetes version is 1.15.</p>

<p>What may be causing that?</p>

<p><strong>Edit 1</strong></p>

<p>Discovered that stackdriver-metadata-agent-cluster-level deployment is CrashLoopBack.</p>

<pre><code>kubectl -n=kube-system logs stackdriver-metadata-agent-cluster-le
vel-f8dcd8b45-nl8dj -c metadata-agent
</code></pre>

<p>Logs from container:</p>

<pre><code>vel-f8dcd8b45-nl8dj  -c metadata-agent
I0408 11:50:41.999214       1 log_spam.go:42] Command line arguments:
I0408 11:50:41.999263       1 log_spam.go:44]  argv[0]: '/k8s_metadata'
I0408 11:50:41.999271       1 log_spam.go:44]  argv[1]: '-logtostderr'
I0408 11:50:41.999277       1 log_spam.go:44]  argv[2]: '-v=1'
I0408 11:50:41.999284       1 log_spam.go:46] Process id 1
I0408 11:50:41.999311       1 log_spam.go:50] Current working directory /
I0408 11:50:41.999336       1 log_spam.go:52] Built on Jun 27 20:15:21 (1561666521)
 at gcm-agent-dev-releaser@ikle14.prod.google.com:/google/src/files/255462966/depot/branches/gcm_k8s_metadata_release_branch/255450506.1/OVERLAY_READONLY/google3
 as //cloud/monitoring/agents/k8s_metadata:k8s_metadata
 with gc go1.12.5 for linux/amd64
 from changelist 255462966 with baseline 255450506 in a mint client based on //depot/branches/gcm_k8s_metadata_release_branch/255450506.1/google3
Build label: gcm_k8s_metadata_20190627a_RC00
Build tool: Blaze, release blaze-2019.06.17-2 (mainline @253503028)
Build target: //cloud/monitoring/agents/k8s_metadata:k8s_metadata
I0408 11:50:41.999641       1 trace.go:784] Starting tracingd dapper tracing
I0408 11:50:41.999785       1 trace.go:898] Failed loading config; disabling tracing: open /export/hda3/trace_data/trace_config.proto: no such file or directory
W0408 11:50:42.003682       1 client_config.go:549] Neither --kubeconfig nor --master was specified.  Using the inClusterConfig.  This might not work.
E0408 11:50:43.999995       1 main.go:110] Will only handle some server resources due to partial failure: unable to retrieve the complete list of server APIs: custom.m
etrics.k8s.io/v1beta1: the server is currently unable to handle the request, custom.metrics.k8s.io/v1beta2: the server is currently unable to handle the request, exter
nal.metrics.k8s.io/v1beta1: the server is currently unable to handle the request
I0408 11:50:44.000286       1 main.go:134] Initiating watch for { v1 nodes} resources
I0408 11:50:44.000394       1 main.go:134] Initiating watch for { v1 pods} resources
I0408 11:50:44.097181       1 main.go:134] Initiating watch for {batch v1beta1 cronjobs} resources
I0408 11:50:44.097488       1 main.go:134] Initiating watch for {apps v1 daemonsets} resources
I0408 11:50:44.098123       1 main.go:134] Initiating watch for {extensions v1beta1 daemonsets} resources
I0408 11:50:44.098427       1 main.go:134] Initiating watch for {apps v1 deployments} resources
I0408 11:50:44.098713       1 main.go:134] Initiating watch for {extensions v1beta1 deployments} resources
I0408 11:50:44.098919       1 main.go:134] Initiating watch for { v1 endpoints} resources
I0408 11:50:44.099134       1 main.go:134] Initiating watch for {extensions v1beta1 ingresses} resources
I0408 11:50:44.099207       1 main.go:134] Initiating watch for {batch v1 jobs} resources
I0408 11:50:44.099303       1 main.go:134] Initiating watch for { v1 namespaces} resources
I0408 11:50:44.099360       1 main.go:134] Initiating watch for {apps v1 replicasets} resources
I0408 11:50:44.099410       1 main.go:134] Initiating watch for {extensions v1beta1 replicasets} resources
I0408 11:50:44.099461       1 main.go:134] Initiating watch for { v1 replicationcontrollers} resources
I0408 11:50:44.197193       1 main.go:134] Initiating watch for { v1 services} resources
I0408 11:50:44.197348       1 main.go:134] Initiating watch for {apps v1 statefulsets} resources
I0408 11:50:44.197363       1 main.go:142] All resources are being watched, agent has started successfully
I0408 11:50:44.197374       1 main.go:145] No statusz port provided; not starting a server
I0408 11:50:45.197164       1 binarylog.go:95] Starting disk-based binary logging
I0408 11:50:45.197238       1 binarylog.go:265] rpc: flushed binary log to ""
</code></pre>

<p><strong>Edit 2</strong></p>

<p>The issue in edit 1 was fixed using the answer in:
<a href="https://stackoverflow.com/a/60549732/4869599">https://stackoverflow.com/a/60549732/4869599</a></p>

<p>But still the hpa can't fetch the metric.</p>

<p><strong>Edit 3</strong></p>

<p>It seems like the issue is caused by <code>custom-metrics-stackdriver-adapter</code> under the <code>custom-metrics</code> namespace which is stuck in <code>CrashLoopBack</code>.</p>

<p>The logs of the machine:</p>

<pre><code>E0419 13:36:48.036494       1 status.go:71] apiserver received an error that is not an metav1.Status: &amp;errors.errorString{s:"http2: stream closed"}
E0419 13:36:48.832653       1 writers.go:172] apiserver was unable to write a JSON response: http2: stream closed
E0419 13:36:48.832692       1 status.go:71] apiserver received an error that is not an metav1.Status: &amp;errors.errorString{s:"http2: stream closed"}
E0419 13:36:49.433150       1 writers.go:172] apiserver was unable to write a JSON response: http2: stream closed
E0419 13:36:49.433191       1 status.go:71] apiserver received an error that is not an metav1.Status: &amp;errors.errorString{s:"http2: stream closed"}
E0419 13:36:51.032656       1 writers.go:172] apiserver was unable to write a JSON response: http2: stream closed
E0419 13:36:51.032694       1 status.go:71] apiserver received an error that is not an metav1.Status: &amp;errors.errorString{s:"http2: stream closed"}
E0419 13:36:51.235248       1 writers.go:172] apiserver was unable to write a JSON response: http2: stream closed
</code></pre>

<p>A related issue:</p>

<p><a href="https://github.com/GoogleCloudPlatform/k8s-stackdriver/issues/303" rel="nofollow noreferrer">https://github.com/GoogleCloudPlatform/k8s-stackdriver/issues/303</a></p>

<p>The problem was with the <code>custom-metrics-stackdriver-adapter</code>. It was crashing in the <code>metrics-server</code> namespace.</p>

<p>Using the resource found here:</p>

<p><a href="https://raw.githubusercontent.com/GoogleCloudPlatform/k8s-stackdriver/master/custom-metrics-stackdriver-adapter/deploy/production/adapter.yaml" rel="nofollow noreferrer">https://raw.githubusercontent.com/GoogleCloudPlatform/k8s-stackdriver/master/custom-metrics-stackdriver-adapter/deploy/production/adapter.yaml</a></p>

<p>And using this image for the deployment (my version was v0.10.2):</p>

<blockquote>
  <p>gcr.io/google-containers/custom-metrics-stackdriver-adapter:v0.10.1</p>
</blockquote>

<p>This fixed the crashing pod, and now the hpa fetch the custom metric.</p>
