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docker-lifecycle.md

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Using the Docker lifecycle with Application Service Adapter

By default, Cloud Foundry and Application Service Adapter uses the Buildpack lifecycle to push applications. To use a pre-built Docker image for an app, specify the Docker lifecycle for the app.

To deploy a Docker image from a container image registry repository, such as Docker Hub, run:

cf push APP_NAME --docker-image REPO/IMAGE:TAG

Differences from Tanzu Application Service

Platform configuration

At the platform level, use of the Docker lifecycle is always available for Application Service Adapter and is not restricted by a feature flag configuration option as in Tanzu Application Service.

Docker app limitations

As with any workload on Kubernetes, running a process as the privileged root user (and conventionally any user with a UID less than 1000) is restricted by default. If a Dockerfile specifies a USER, it must have a defined UID. You can either specify a numeric value for the USER or RUN the useradd command with the --uid option.

For example, to set the user to "appuser" while still ensuring the UID is both defined and unprivileged, you could use the following Dockerfile:

FROM ubuntu:latest
RUN useradd -r -u 1001 -g appuser appuser
USER appuser
...

Port configuration

Tanzu Application Service expects that applications listen on the port specified by the PORT environment variable. Application Service Adapter, however, expects that all applications listen on port 8080 to handle HTTP requests. Docker images can configure alternative ports through the EXPOSE directive in the Dockerfile. Application Service Adapter discovers this port configuration from the image and configures the default route accordingly.

When the EXPOSE directive is missing from the Dockerfile, and the app is listening on a port other than 8080, you can use the following procedure to configure the app route with the appropriate port:

APP_NAME=<your app name>
DOMAIN=<the domain name>
IMAGE=<repo/image:tag>
DESIRED_PORT=<app port>

cf push $APP_NAME --no-route --docker-image $IMAGE
cf create-route $DOMAIN --hostname $APP_NAME
route_guid=$(cf curl /v3/routes | jq -r ".resources[] | select(.host==\"$APP_NAME\").guid")
read -r -d '' destination <<EOF
{
   "destinations": [
   {
     "app": {
       "guid": "$(cf app $APP_NAME --guid)",
       "process": {
         "type": "web"
       }
     },
     "port": $DESIRED_PORT,
     "protocol": "http1"
   }
 ]
}
EOF
cf curl -XPOST "/v3/routes/$route_guid/destinations" -d "$destination"