kubernetes-go-configmap-rollout

App Rollout via ConfigMap Data Change

Uses nginx to reverse-proxy traffic to pulumi.github.io. The nginx configuration is contained in the file default.conf in this directory; this program reads that file and puts it in a ConfigMap. Hence, changing data in that file will cause register as a change in the ConfigMap's data, which will trigger a rollout of the nginx Deployment.

Running the App

Follow the steps in Pulumi Installation and Setup and Configuring Pulumi Kubernetes to get setup with Pulumi and Kubernetes.

Install dependencies:

go mod download

Create a new stack:

$ pulumi stack init
Enter a stack name: configmap-rollout-dev

This example will attempt to expose the nginx deployment to the Internet with a Service of type LoadBalancer. Since minikube does not support LoadBalancer, the application already knows to use type ClusterIP instead; all you need to do is to tell it whether you're deploying to minikube:

pulumi config set isMinikube <value>

Perform the deployment:

$ pulumi up
Updating stack 'configmap-rollout-dev'
Performing changes:

     Type                           Name                                     Status      Info
 +   pulumi:pulumi:Stack            configmap-rollout-configmap-rollout-dev  created
 +   ├─ kubernetes:core:ConfigMap   nginx                                    created
 +   ├─ kubernetes:apps:Deployment  nginx                                    created
 +   └─ kubernetes:core:Service     nginx                                    created

---outputs:---
frontendIp: "35.193.210.254"

info: 4 changes performed:
    + 4 resources created
Update duration: 49.612528861s

Permalink: https://app.pulumi.com/hausdorff/configmap-rollout-dev/updates/1

We can see here in the ---outputs:--- section that our proxy was allocated a public IP, in this case 35.193.210.254. It is exported with a stack output variable, frontendIp. We can use curl and grep to retrieve the <title> of the site the proxy points at.

$ curl -sL $(pulumi stack output frontendIp):80 | grep -C 1 "<title>"

    <title>Pulumi. Serverless // Containers // Infrastructure // Cloud // DevOps</title>

Now, open default.conf and change .node.server and .server.location.proxy_set_header to point at google.com. If you're on macOS you can run sed -i bak "s/pulumi.github.io/google.com/g" default.conf

The result should look like this:

upstream node {
  server google.com;
}
server {
  listen                  80;
  server_name             _;
  root                    /usr/share/nginx/html;
  location / {
    proxy_set_header X-Real-IP \$remote_addr;
    proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for;
    proxy_set_header Host google.com;
    proxy_pass http://node;
    proxy_redirect off;
    port_in_redirect off;
  }
}

Running preview now shows that this change will cause us to replace the ConfigMap with a new one containing the new data, and subsequently trigger a rollout in the Deployment.

NOTE: This rollout is safe! Pulumi executes this plan with the following steps:

1. Create a new ConfigMap with a new name and the new data.
2. Update the PodTemplate of the Deployment to point at the new ConfigMap. This update triggers the Deployment controller to try to roll out a new set of containers with mounts that contain this new data.
3. Only once that succeeds, delete the old ConfigMap.

Previewing update of stack 'configmap-rollout-dev'
     Type                           Name                                     Status        Info
 *   pulumi:pulumi:Stack            configmap-rollout-configmap-rollout-dev  no change
 +-  ├─ kubernetes:core:ConfigMap   nginx                                    replace       changes: ~ data,metadata
 ~   └─ kubernetes:apps:Deployment  nginx                                    update        changes: ~ spec

info: 2 changes previewed:
    ~ 1 resource to update
    +-1 resource to replace
      2 resources unchanged

Running pulumi up should similarly look something like this:

Updating stack 'configmap-rollout-dev'
     Type                           Name                                     Status       Info
 *   pulumi:pulumi:Stack            configmap-rollout-configmap-rollout-dev  done
 +-  ├─ kubernetes:core:ConfigMap   nginx                                    replaced     changes: ~ data,metadata
 ~   └─ kubernetes:apps:Deployment  nginx                                    updated      changes: ~ spec

---outputs:---
frontendIp: "35.193.210.254"

info: 2 changes performed:
    ~ 1 resource updated
    +-1 resource replaced
      2 resources unchanged
Update duration: 5.679919856s

Permalink: https://app.pulumi.com/hausdorff/configmap-rollout-dev/updates/13

Now, if we curl the IP address once more, we see that it points at google.com!

Note: minikube does not support type LoadBalancer; if you are deploying to minikube, make sure to run kubectl port-forward svc/frontend 8080:80 to forward the cluster port to the local machine and access the service via localhost:8080.

$ curl -sL $(pulumi stack output frontendIp) | grep -o "<title>Google</title>"
<title>Google</title>