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Lab 2: Docker

Exploring Docker container registries

Every docker image is build upon a base image which is defined in the Dockerfile.

Now, let's try to find the base image from the following Dockerfile:

FROM registry.access.redhat.com/ubi8/nodejs-10

# Change working directory
WORKDIR /opt/app-root/src/

# Install npm production packages
COPY package*.json /opt/app-root/src/
RUN cd /opt/app-root/src; npm ci

COPY . /opt/app-root/src/

ENV NODE_ENV production
ENV PORT 3000

EXPOSE 3000

CMD ["npm", "start"]

Have a look at the Dockerfile of the base image!

Hint: There are two well known public container registries:

Be aware, that everybody can upload images to Docker Hub, so use them with caution! All the images from the redhat registry are certified and should be used whenever possible.

Now, explore the container registry. Do you find an image that you might use for one of your own applications?

Build an application on OpenShift from a Dockerfile

After exploring the registries, let's acutally build an application from a Dockerfile.

For this purpose the oc command oc new-build is utilized.

The application that is being build is a simple http server, based on this git repository: https://github.com/sclorg/httpd-container

First, open the repository and locate the Dockerfile in the 2.4 folder. Second, open the file and have a look at the individual steps.

Now open a terminal, log into your OpenShift cluster, select your project and execute the following command:

oc new-build https://github.com/sclorg/httpd-container --context-dir 2.4/ --strategy docker

The command created a BuildConfig called httpd-container and starts a new build httpd-container-1.

Have a look at the progress of the build by executing:

oc build-logs httpd-container-1

For newer versions of the OpenShift CLI you need to run the following command:

oc logs build/httpd-container-1

Now you can see how each step of the Dockerfile is executed and several layers are built. At the end the resulting image is pushed to the internal image registry and could now be started up as a container.

Hint: To start a new build use the command oc start-build httpd-container or navigate to the Build section in the UI, click on the BuildConfig and select Start Build