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150 lines
3.8 KiB
Markdown
150 lines
3.8 KiB
Markdown
# Demo: Injecting k8s runtime data into containers
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In this tutorial, you will learn how to use `kustomize` to declare a variable reference and substitute it in container's command. Note that, the substitution is not for arbitrary fields, it is only applicable to container env, args and command.
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To run WordPress, it's necessary to
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- connect WordPress with a MySQL database
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- access the service name of MySQL database from WordPress container
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First make a place to work:
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<!-- @makeDemoHome @testAgainstLatestRelease -->
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```
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DEMO_HOME=$(mktemp -d)
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MYSQL_HOME=$DEMO_HOME/mysql
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mkdir -p $MYSQL_HOME
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WORDPRESS_HOME=$DEMO_HOME/wordpress
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mkdir -p $WORDPRESS_HOME
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```
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### Download resources
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Download the resources and `kustomization.yaml` for WordPress.
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<!-- @downloadResources @testAgainstLatestRelease -->
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```
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CONTENT="https://raw.githubusercontent.com\
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/kubernetes-sigs/kustomize\
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/master/examples/wordpress/wordpress"
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curl -s -o "$WORDPRESS_HOME/#1.yaml" \
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"$CONTENT/{deployment,service,kustomization}.yaml"
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```
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Download the resources and `kustomization.yaml` for MySQL.
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<!-- @downloadResources @testAgainstLatestRelease -->
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```
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CONTENT="https://raw.githubusercontent.com\
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/kubernetes-sigs/kustomize\
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/master/examples/wordpress/mysql"
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curl -s -o "$MYSQL_HOME/#1.yaml" \
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"$CONTENT/{deployment,service,secret,kustomization}.yaml"
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```
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### Create kustomization.yaml
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Create a new kustomization with two bases,
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`wordpress` and `mysql`:
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<!-- @createKustomization @testAgainstLatestRelease -->
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```
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cat <<EOF >$DEMO_HOME/kustomization.yaml
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resources:
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- wordpress
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- mysql
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namePrefix: demo-
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patches:
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- path: patch.yaml
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EOF
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```
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### Download patch for WordPress
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In the new kustomization, apply a patch for wordpress deployment. The patch does two things
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- Add an initial container to show the mysql service name
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- Add environment variable that allow wordpress to find the mysql database
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<!-- @downloadPatch @testAgainstLatestRelease -->
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```
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CONTENT="https://raw.githubusercontent.com\
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/kubernetes-sigs/kustomize\
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/master/examples/wordpress"
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curl -s -o "$DEMO_HOME/#1.yaml" \
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"$CONTENT/{patch}.yaml"
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```
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The patch has following content
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> ```
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> apiVersion: apps/v1
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> kind: Deployment
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> metadata:
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> name: wordpress
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> spec:
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> template:
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> spec:
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> initContainers:
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> - name: init-command
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> image: debian
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> command: ["/bin/sh"]
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> args: ["-c", "echo $(WORDPRESS_SERVICE); echo $(MYSQL_SERVICE)"]
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> containers:
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> - name: wordpress
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> env:
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> - name: WORDPRESS_DB_HOST
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> value: $(MYSQL_SERVICE)
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> - name: WORDPRESS_DB_PASSWORD
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> valueFrom:
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> secretKeyRef:
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> name: mysql-pass
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> key: password
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> ```
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The init container's command requires information that depends on k8s resource object fields, represented by the placeholder variables
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$(WORDPRESS_SERVICE) and $(MYSQL_SERVICE).
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### Bind the Variables to k8s Object Fields
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<!-- @addVarRef @testAgainstLatestRelease -->
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```
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cat <<EOF >>$DEMO_HOME/kustomization.yaml
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vars:
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- name: WORDPRESS_SERVICE
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objref:
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kind: Service
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name: wordpress
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apiVersion: v1
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fieldref:
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fieldpath: metadata.name
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- name: MYSQL_SERVICE
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objref:
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kind: Service
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name: mysql
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apiVersion: v1
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EOF
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```
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`WORDPRESS_SERVICE` is from the field `metadata.name` of Service `wordpress`. If we don't specify `fieldref`, the default is `metadata.name`. So `MYSQL_SERVICE` is from the field `metadata.name` of Service `mysql`.
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### Substitution
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Confirm the variable substitution:
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<!-- @kustomizeBuild @testAgainstLatestRelease -->
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```
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kustomize build $DEMO_HOME
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```
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Expect this in the output:
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> ```
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> (truncated)
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> ...
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> initContainers:
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> - args:
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> - -c
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> - echo demo-wordpress; echo demo-mysql
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> command:
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> - /bin/sh
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> image: debian
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> name: init-command
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>
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> ```
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