Example to demonstrate How Helm Chart Hooks works

What is a Helm Chart Hooks?

1. Using hooks chart developers can either execute logic or create Kubernetes objects at a certain point in the release life cycle.
2. For e.g., Creating a secret pre-install or Taking a backup of database pre-upgrade.
3. Hooks are like any other template like Pod, Deployment, etc. Helm identifies between a Hook and any other template using helm.sh/hook annotation.

Types of Hooks

Hooks Deletion Policies

Hooks Execution Order

How are Hooks considered to be ready?

1. If hooks are Pods or Jobs, then hooks become ready once Pods or Jobs are completed.
2. If hooks are any other Kubernetes objects other than Pods and Jobs, then hooks become ready as soon as those objects are loaded or updated.

Example

Prerequisite

1. Clone helm-chart-hooks-example GitHub repository by running the following command:

   git clone https://github.com/sagar-jadhav/helm-chart-hooks-example.git
   

2. Move to helm-chart-hooks-example directory by running the following command:

   cd ./helm-chart-hooks-example
   

3. log in to Docker Hub by running the following command:

   docker login -u <Username>
   

   Where:

   • <Username> is the username to log in to the docker hub.

4. Create the repositories in Docker Hub with the following names:

   • post-install-db-init
   • post-upgrade-add-data

5. Move to post-install-init-db directory by running the following command:

   cd ./post-install-init-db
   

6. Build post-install job docker image by running the following command:

   docker build -t post-install-db-init:1.0.0 .
   

7. Tag post-install job docker image by running the following command:

   docker tag post-install-db-init:1.0.0 <Username>/post-install-db-init:1.0.0
   

   Where:

   • <Username> is the username to log in to the docker hub.

8. Push post-install job docker image by running the following command:

   docker push <Username>/post-install-db-init:1.0.0
   

   Where:

   • <Username> is the username to log in to the docker hub.

9. Move out of post-install-init-db directory by running the following command:

   cd ..
   

10. Move to post-upgrade-add-data by running the following command:

cd ./post-upgrade-add-data

11. Build post-upgrade job docker image by running the following command:

    docker build -t post-upgrade-add-data:1.0.0 .
    

12. Tag post-upgrade job docker image by running the following command:

    docker tag post-upgrade-add-data:1.0.0 <Username>/post-upgrade-add-data:1.0.0
    

    Where:

    • <Username> is the username to log in to the docker hub.

13. Push post-upgrade job docker image by running the following command:

     docker push <Username>/post-upgrade-add-data:1.0.0
    

    Where:

    • <Username> is the username to log in to the docker hub.

14. Move out of post-upgrade-add-data directory by running the following command:

    cd ..
    

15. Provision a single-node Kubernetes cluster.

16. Create the following directories in the Kubernetes node:

    • /root/db-data
    • /root/share
    • /root/scripts

17. Replace <DockerHub Username> with the username to log in to the docker hub in values.yaml file located at <Path to helm-chart-hooks-example>/mysql/values.yaml location.

18. Create a file with name rename-backup.sh at /root/share/post-backup location and add the following content into it:

    #!/bin/bash
    # Rename backup file.
    if [[ -n "$DB_DUMP_DEBUG" ]]; then
      set -x
    fi
    
    if [ -e ${DUMPFILE} ];
    then
     new_name=mysql-backup.gz
     old_name=$(basename ${DUMPFILE})
     echo "Renaming backup file from ${old_name} to ${new_name}"
     cp ${DUMPFILE} /db/${new_name}
    else
     echo "ERROR: Backup file ${DUMPFILE} does not exist!"
    fi
    

Demo

1. Install the MySQL application by running the following command:

   helm install mysql ./mysql/
   

   Wait for some time for the command to get executed successfully.

2. Verify that data got populated in the database by running the following command:

   kubectl exec -it <MySQL Pod Name> -n mysql -- /bin/bash
   

   mysql -hmysql -uroot -padmin
   

   Use Universe;
   

   Select * From Heroes;
   

   exit
   

   exit
   

   Where:

   • <MySQL Pod Name> is the MySQL Pod name, You can get the MySQL Pod name using the kubectl get po -n mysql command.

3. Upgrade the MySQL application by running the following command:

   helm upgrade mysql ./mysql/
   

   Wait for some time for the command to get executed successfully.

4. Verify that data got populated in database post upgrade by running the following command:

   kubectl exec -it <MySQL Pod Name> -n mysql -- /bin/bash
   

   mysql -hmysql -uroot -padmin
   

   Use Universe;
   

   Select * From Heroes;
   

   exit
   

   exit
   

   Where:

   • <MySQL Pod Name> is the MySQL Pod name, You can get the MySQL Pod name using kubectl get po -n mysql command.

5. Rollback the MySQL application by running the following command:

   helm rollback mysql 1
   

   Wait for some time for the command to get executed successfully.

6. Verify that data got corrected in the database post rollback by running the following commands:

   kubectl exec -it <MySQL Pod Name> -n mysql -- /bin/bash
   

   mysql -hmysql -uroot -padmin
   

   Use Universe;
   

   Select * From Heroes;
   

   exit
   

   exit
   

   Where:

   • <MySQL Pod Name> is the MySQL Pod name, You can get the MySQL Pod name using kubectl get po -n mysql command.

7. Delete the MySQL application by running the following command:

   helm uninstall mysql
   

   Wait for some time for the command to get executed successfully.