Tutorial: Docker Compose update

In this tutorial, we will conduct a container update to a device using a multi-container Docker composition with a Traefik gateway and a backend service whoami. First we will create the update Artifact with a new Docker composition and deploy it to the device. In the second part will show how update the Docker images in the composition using binary delta to save size and data transfer bandwidth.

Prerequesites

To get started using the Docker Compose Update Module, we need to prepare the target devices for accepting the deployment and the workstation for creating the deployment.

Prepare the devices

Before installing the Update Module on the target device, you need to ensure that the following dependencies are installed on the device:

• Mender client (version >= 3.0)
• Docker Engine
• Docker Compose (version >= 2.0)
• jq
• xdelta3

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

mender --version && \
  docker --version && \
  docker compose version && \
  xdelta3 -V && \
  jq --version

To install the Docker Compose Update Module, 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/master/src/app \
        -O /usr/share/mender/modules/v3/app \
        && chmod +x /usr/share/mender/modules/v3/app
# Install Docker Compose module
mkdir -p /usr/share/mender/app-modules/v1
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/master/src/app-modules/docker-compose \
        -O /usr/share/mender/app-modules/v1/docker-compose \
        && chmod +x /usr/share/mender/app-modules/v1/docker-compose
# Install the Configuration files
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/master/conf/mender-app.conf \
        -O /etc/mender/mender-app.conf
wget https://raw.githubusercontent.com/mendersoftware/app-update-module/master/conf/mender-app-docker-compose.conf \
        -O /etc/mender/mender-app-docker-compose.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/master/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 Docker Compose manifest and the Docker images used by the composition. Including the Docker images is optional, excluding the images will make the devices try to pull the images from the Docker registry.

Create the Mender artifact

Begin by creating the manifest on your workstation and saving it in a separate directory:

mkdir -p manifests/v1
cat <<EOF > manifests/v1/docker-compose.yaml
version: "3.3"
services:
  gateway:
    image: "traefik:v2.9"
    command:
      - "--providers.docker=true"
      - "--providers.docker.exposedbydefault=false"
      - "--entrypoints.web.address=:80"
    ports:
      - "8080:80"
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock:ro"
  whoami:
    image: "traefik/whoami"
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.whoami.rule=Path(\`/whoami\`)"
      - "traefik.http.routers.whoami.entrypoints=web"
EOF

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/traefik:v2.9 \
        --image docker.io/traefik/whoami:latest \
        --orchestrator docker-compose \
        --manifests-dir ./manifests/v1 \
        --output-path artifact.mender \
        -- \
        --software-name="$ARTIFACT_NAME" \
        --software-version="v1"

constraints](../../09.Software-versioning/docs.md#application-updates-update-modules) to !!!!! prevent deploying the wrong version to a device.

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

Once deployed, the device will start serving a simple server on port 8080. You can test the application by sending a request to path /whoami and the server will echo the request. To this end, we will leverage the Troubleshoot add-on and start a port-forward session using the mender-cli.

mender-cli port-forward <device_id> 8080:8080

curl http://localhost:8080/whoami

Hostname: d8ae8a9eca1c
IP: 127.0.0.1
IP: 172.19.0.3
RemoteAddr: 172.19.0.2:58470
GET /whoami HTTP/1.1
Host: localhost:8080
Accept: */*
Accept-Encoding: gzip
X-Forwarded-For: 172.19.0.1
X-Forwarded-Host: localhost:8080
X-Forwarded-Port: 8080
X-Forwarded-Proto: http
X-Forwarded-Server: c2c36ac1634b
X-Real-Ip: 172.19.0.1

Update your composition using delta

Now that your Docker composition is running on the device, it is time to upgrade the Traefik container to the next version. Create a new manifest directory and bump gateway service to traefik:v2.10:

mkdir -p manifests/v2
cat <<EOF > manifests/v2/docker-compose.yaml
version: "3.3"
services:
  gateway:
    image: "traefik:v2.10"
    command:
      - "--providers.docker=true"
      - "--providers.docker.exposedbydefault=false"
      - "--entrypoints.web.address=:80"
    ports:
      - "8080:80"
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock:ro"
  whoami:
    image: "traefik/whoami"
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.whoami.rule=Path(\`/whoami\`)"
      - "traefik.http.routers.whoami.entrypoints=web"
EOF

Since we are only upgrading the Traefik service, we do not need to include the image for the whoami service since this was provided by the last deployment. And, to save bandwidth we will create a binary delta of the image for the gateway service.

app-gen --artifact-name "${ARTIFACT_NAME}-v2" \
        --device-type "$DEVICE_TYPE" \
        --platform "$PLATFORM" \
        --application-name "$ARTIFACT_NAME" \
        --image docker.io/library/traefik:v2.9,docker.io/library/traefik:v2.10 \
        --orchestrator docker-compose \
        --manifests-dir ./manifests/v2 \
        --output-path artifact-v2.mender \
        --deep-delta \
        -- \
        --software-name "${ARTIFACT_NAME}" \
        --software-version "v2" \
        --depends "rootfs-image.${ARTIFACT_NAME}.version:v1"

The --deep-delta flag enables the delta feature which creates a binary delta between the container images provided by the --image flag. Note that the --image flag needs two inputs to be able to compute the delta. After generating the artifact, upload the artifact to the Mender server and deploy it to your device.

Congratulations! You successfully upgraded a component on your device. Continue reading to learn more about advanced use-cases such as custom update modules) and software versioning.