stevenaldinger/docker-k8s-wait-for-it repository overview

⁠Wait for It Init Container

This container's job is to stall a deployment from running any containers until some network conditions are met.

⁠Config environment variables

This image checks for and matches the conditions listed below (in order) before allowing the other containers in the deployment to run.

1 WAIT_FOR_IT

• form: "true" or "false"

• must equal "true" or the init container will be ignored

• examples:

  WAIT_FOR_IT="true"
  

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  WAIT_FOR_IT="false"
  

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2 WAIT_FOR_PODS

• Waits for other service's pods to be running before containers can start

• form: <service-name>.<namespace>;<service-name-2>.<namespace-2>

• examples:

  WAIT_FOR_PODS="mysql.test"
  

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  WAIT_FOR_PODS="mysql.test;kube-dns.kube-system"
  

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1. WAIT_FOR_EXTERNAL_IPS

• Waits for a k8s service to have an exposed external IP (not <pending> or ClusterIP)

• form: <service-name>.<namespace>;<service-name-2>.<namespace-2>

• examples:

  WAIT_FOR_EXTERNAL_IPS="nginx.test"
  

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  WAIT_FOR_EXTERNAL_IPS="nginx.test;otherservice.default"
  

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1. WAIT_FOR_DNS_MATCHES

• Waits for a domain name to match a specific IP before continuing

• form: <domain-name>=<ip-address>;<domain-name-2>=<ip-address-2>

• examples:

  WAIT_FOR_DNS_MATCHES="drone.grinsides.com=35.237.17.14;grinsides.com=35.237.17.15"
  

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⁠Handle Kubernetes Services Dependencies

If you need to make sure a database is running before starting a GUI pod, this is the init container for you.

To wait for:

1. mysql pod to start in databases namespace
2. mongo pod to start in othernamespace namespace
3. redis pod to start in anothernamespace namespace

Configure an init container in your deployment like this:

initContainers:
- name: "wait-for-services"
  image: stevenaldinger/docker-k8s-wait-for-it
  imagePullPolicy: Always
  env:
  - name: WAIT_FOR_IT
    value: "true"
  - name: WAIT_FOR_PODS
    value: "mysql.databases;mongo.othernamespace;redis.anothernamespace"
  - name: WAIT_FOR_EXTERNAL_IPS
    value: "nginx.proxy"
  - name: WAIT_FOR_DNS_MATCHES
    value: "drone.grinsides.com=35.237.17.14;grinsides.com=35.237.17.15"

⁠While testing:

Run this to view init logs:

kubectl logs -f $(kubectl get po -l app=redis -o jsonpath='{.items[0].metadata.name}') -c redis-init

Run this to bash into init container:

kubectl exec -it $(kubectl get po -l app=redis -o jsonpath='{.items[0].metadata.name}') -c redis-init bash