Container Basics

Understanding the Dockerfile

A Dockerfile describes how the container is supposed to be constructed. It's a bit like setting up software on a machine: you specify the steps to copy stuff around, install a package or maybe even build stuff from source. Let's have a look at a simple example, a Node.js app:

FROM mhart/alpine-node:8
MAINTAINER Michael Hausenblas 
WORKDIR /app
COPY dok-example-us/stock-con/ .
RUN npm install express && \
    npm install
USER nobody:nobody
CMD ["node", "service.js"]

Now, paste above content—see the copy icon in the upper-right corner of above block—and it will be automatically saved in a file called (surprise!) Dockerfile in the current directory.

Building a container image

Now we'll build the container image. Note that you really should assign a sensible tag here, never use latest (same if you don't specify a tag):

docker build -t $YOUR_IMAGE_NAME .

Above, replace the $YOUR_IMAGE_NAME with the name of your image. For example, Michael's would look as follows:

docker build -t quay.io/mhausenblas/stock-con:tcw0 .

Did it work? Well, let's check:

docker images

Also, before you proceed make sure that you see an image called quay.io/mhausenblas/stock-gen:0.3 in the images, there. This one is pulled in the background and you can only do the next step if this one is present.

Running a container

Next you will create a container based on the image you created in the previous step:

docker run --rm --name stock-con -p 8080:9898 --link stock-gen:stock-gen -e DOK_STOCKGEN_PORT=9876 -e DOK_STOCKGEN_HOSTNAME=stock-gen $YOUR_IMAGE_NAME

Again, make sure that you replace the $YOUR_IMAGE_NAME with whatever you selected for your image name (incl. a tag).

Now, you can check if it worked correctly by issuing the following command in a new terminal session (click the + button):

curl localhost:8080/average/NYSE:RHT

Or, you can click on the Web Preview pane and whatever URL comes up there, you append average/NYSE:RHT.

Using a container registry

Finally, if you have access to a container registry—we suggest you sign up at quay.io but Dockerhub will also do—then you can also push the container image you built locally to that registry. If it's a public container image repo, all of your friends and colleagues can readily use it after you've pushed it.

docker push $YOUR_IMAGE_NAME

So the full image name $YOUR_IMAGE_NAME would be something along the line of:

$CONTAINER_REGISTRY/$USER/$IMAGE:$TAG

Note that above structure doesn't have to look like this, different registries expose different conventions but Michael's using quay.io and this one follows the above structure (As do many others).

As a bonus challenge: when you're done with pushing your image, share the URL with your neighbor who could then do a docker pull … and run your image ;)

cd <directory>	Change directory
ls	List directory
echo 'contents' > <file>	Write contents to a file
cat <file>	Output contents of file

i	In Command Mode	Change into Insert Mode, you can now insert and edit text in the file
esc	In Insert Mode	Change into Command Mode, you can now execute commands
:wq	In Command Mode	Save and Exit

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tcw - Container Basics

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