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64 lines
2.7 KiB
Markdown
64 lines
2.7 KiB
Markdown
# Hunting flaky tests in Kubernetes
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Sometimes unit tests are flaky. This means that due to (usually) race conditions, they will occasionally fail, even though most of the time they pass.
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We have a goal of 99.9% flake free tests. This means that there is only one flake in one thousand runs of a test.
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Running a test 1000 times on your own machine can be tedious and time consuming. Fortunately, there is a better way to achieve this using Kubernetes.
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_Note: these instructions are mildly hacky for now, as we get run once semantics and logging they will get better_
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There is a testing image ```brendanburns/flake``` up on the docker hub. We will use this image to test our fix.
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Create a replication controller with the following config:
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```yaml
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apiVersion: v1
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kind: ReplicationController
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metadata:
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name: flakecontroller
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spec:
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replicas: 24
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template:
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metadata:
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labels:
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name: flake
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spec:
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containers:
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- name: flake
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image: brendanburns/flake
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env:
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- name: TEST_PACKAGE
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value: pkg/tools
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- name: REPO_SPEC
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value: https://github.com/GoogleCloudPlatform/kubernetes
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```
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Note that we omit the labels and the selector fields of the replication controller, because they will be populated from the labels field of the pod template by default.
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```./cluster/kubectl.sh create -f controller.yaml```
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This will spin up 24 instances of the test. They will run to completion, then exit, and the kubelet will restart them, accumulating more and more runs of the test.
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You can examine the recent runs of the test by calling ```docker ps -a``` and looking for tasks that exited with non-zero exit codes. Unfortunately, docker ps -a only keeps around the exit status of the last 15-20 containers with the same image, so you have to check them frequently.
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You can use this script to automate checking for failures, assuming your cluster is running on GCE and has four nodes:
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```sh
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echo "" > output.txt
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for i in {1..4}; do
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echo "Checking kubernetes-minion-${i}"
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echo "kubernetes-minion-${i}:" >> output.txt
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gcloud compute ssh "kubernetes-minion-${i}" --command="sudo docker ps -a" >> output.txt
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done
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grep "Exited ([^0])" output.txt
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```
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Eventually you will have sufficient runs for your purposes. At that point you can stop and delete the replication controller by running:
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```sh
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./cluster/kubectl.sh stop replicationcontroller flakecontroller
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```
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If you do a final check for flakes with ```docker ps -a```, ignore tasks that exited -1, since that's what happens when you stop the replication controller.
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Happy flake hunting!
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[]()
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