Tutorial: Kubernetes update

In this tutorial, we will conduct a Kubernetes manifest based update to a device with a python application and PostgreSQL database. We will create the update Artifact with a new manifest and deploy it to the device.

Prerequisites

To get started using the Application Update Module for kubernetes-based applications we need to perform certain configuration operations.

Prepare the devices

Before installing the Update Module on the target device, you need to install and configure the following utilities on the device:

• Mender Client (version >= 3.0)
• kubectl
• jq
• tree
• xdelta3 (optional)

To quickly verify the required dependencies are installed on your device, run the following commands:

mender --version && \
  kubectl version && \
  jq --version && \
  tree --version

We understand the existence of configured kubectl command as a proof that you have configured kubernetes of any flavour, and we will not focus on the installation but assume that kubectl presents a working interface to your cluster.

To install the Application Update Module and the Kubernetes submodule, you need to run the following commands on your devices:

# Install Application Update Module
mkdir -p /usr/share/mender/modules/v3
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/1.0.0/src/app \
        -O /usr/share/mender/modules/v3/app \
        && chmod +x /usr/share/mender/modules/v3/app
# Install Kubernetes submodule
mkdir -p /usr/share/mender/app-modules/v1
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/1.0.0/src/app-modules/k8s \
        -O /usr/share/mender/app-modules/v1/k8s \
        && chmod +x /usr/share/mender/app-modules/v1/k8s
# Install the Configuration files
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/1.0.0/conf/mender-app.conf \
        -O /etc/mender/mender-app.conf
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/1.0.0/conf/mender-app-k8s.conf \
        -O /etc/mender/mender-app-k8s.conf

Prepare the workstation

Once your devices are ready, return to your workstation and install the Application Update Artifact Generator. First, make sure that you have mender-artifact (version >= 3.0) installed on your workstation, then install the Application Update Artifact Generator:

BINDIR=$HOME/bin
mkdir -p $BINDIR
export PATH=$BINDIR:$PATH
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/1.0.0/gen/app-gen \
        -O $BINDIR/app-gen
chmod +x $BINDIR/app-gen

Create a deployment

The app-gen script we installed previously extends the mender-artifact tool to create Artifacts for container updates. We will use this tool to create a Mender Artifact containing the Kubernetes manifest and the images used by the composition.

Create the Mender artifact

In order to create a kubernetes-based application update module Mender artifact we will prepare the following directory structure:

manifests/v1/
├── deployments
│   ├── app.yaml
│   └── postgres.yaml
├── secrets
│   └── secret-postgres.yaml
└── services
    └── service-postgres.yaml

4 directories, 4 files

And with the following contents:

==> manifests/v1/deployments/app.yaml <==
apiVersion: apps/v1
kind: Deployment
metadata:
  name: python-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: python-container
  template:
    metadata:
      labels:
        app: python-container
        tier: backend
    spec:
      containers:
        - name: python-container
          image: python:latest

==> manifests/v1/deployments/postgres.yaml <==
apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: postgres-container
  template:
    metadata:
      labels:
        app: postgres-container
        tier: backend
    spec:
      containers:
        - name: postgres-container
          image: postgres:15.4
          env:
            - name: POSTGRES_USER
              valueFrom:
                secretKeyRef:
                  name: postgres-secret
                  key: user

            - name: POSTGRES_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: postgres-secret
                  key: password

            - name: POSTGRES_DB
              value: db0

          ports:
            - containerPort: 5432

==> manifests/v1/secrets/secret-postgres.yaml <==
apiVersion: v1
kind: Secret
metadata:
  name: postgres-secret
type: Opaque
data:
  user: dXNlcjA=
  password: bG9uZ3Bhc3N3b3Jk

==> manifests/v1/services/service-postgres.yaml <==
kind: Service
apiVersion: v1
metadata:
  name: postgres-service
spec:
  selector:
    app: postgres-container
  ports:
    - protocol: TCP
      port: 5432
      targetPort: 5432

To generate the artifact, we need to know the target platform of the devices we want to deploy to. In the following example, we will assume the platform we are deploying to is linux/arm/v7 (os/arch/variant). You can check more details regarding this notation in Multi-platform images and Architectures other than amd64.

ARTIFACT_NAME="myfirstcomposition"
DEVICE_TYPE="raspberrypi4"
PLATFORM="linux/arm/v7"
app-gen --artifact-name "$ARTIFACT_NAME" \
        --device-type "$DEVICE_TYPE" \
        --platform "$PLATFORM" \
        --application-name "$ARTIFACT_NAME" \
        --image docker.io/library/postgres:15.1 \
        --image docker.io/library/python:latest \
        --orchestrator k8s \
        --manifests-dir ./manifests/v1 \
        --output-path artifact.mender \
        -- \
        --software-name="$ARTIFACT_NAME" \
        --software-version="v1"

Deploy the Mender Artifact

The generated artifact is now ready to be deployed on the device. Open your browser and navigate to the "Releases" column in Hosted Mender UI and upload your newly created artifact. Once uploaded, navigate to the "Devices" column and select your device and then click Create a deployment for this device in the Device actions in the bottom right corner. Select your newly created artifact and click CREATE DEPLOYMENT.

Verify your deployment

You can use the kubectl command on the device to verify that the pods are running:

 # kubectl get pods
NAME                                   READY   STATUS                   RESTARTS   AGE
python-deployment-567c5dbcbd-6k57l     1/1     Running                  0          20m
postgres-deployment-7b54fd68f9-8fkhj   1/1     Running                  0          20m