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Tutorial: Graceful app rollout

In this tutorial, we’ll use 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.

configmapRollout

Running the App

First, download the code here.

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

Install dependencies:

npm install

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>