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0. Setup

• Docker CE for Ubuntu
• Docker for Mac

docker -v should return Docker version 17.12.0-ce, ...

1. Containers

docker run hello-world

Show daemon running on host.

Hello world image

docker run -it ubuntu /bin/bash will start a shell running inside an Ubuntu container.

Notice how the image is downloaded automatically, layer by layer.

ps -fe will show the namespaced process tree inside the container. How long do you expect the output to be?

docker exec -it $container /bin/bash will open another shell in the same container.

What happens if I run vim /tmp/new_file.txt?

What happens if I run touch /tmp/new_file.txt, exit the container and start a new one?

2. Container images

docker build -f Dockerfile.hello -t elifesciences/hello . will build a local image tagged elifesciences/hello. Take a look at the [Dockerfile.

docker run elifesciences/hello will run the default command of the image, which is a cat command.

What do I have to do if I want to run this code on another laptop?

3. Users

docker run -it -u 33 elifesciences/hello /bin/bash runs a shell for the www-data standard user, which is unprivileged.

What happens when I run echo "IMPACT FACTOR" > message.txt?

4. Volumes

docker run -it -v $(pwd):/code elifesciences/hello /bin/bash will run a container where the current folder is mounted as a volume. Incidentally, it also means the volume's content will persist beyond the lifetime of the container.

mount | grep /code will show the mount point.

What does ls -ld /code shows? What does that 1000 (or other number) mean?

Can I touch /code/42.txt?

5. Base images

docker build -f Dockerfile.derived -t elifesciences/hello . will create an image derived from our own base PHP CLI image.

docker run elifesciences/hello will now use the new image, try it.

But what if we want to use local modifications? Without rebuilding the container every time we save a file?

Make a local change. What happens when I run docker run -v $(pwd)/hello.php:/srv/hello/hello.php elifesciences/hello?

6. Ports

Run docker run -p 8003:8003 elifesciences/hello php -S 0.0.0.0:8003 -t . to start a PHP container listening on port 8003 for HTTP connections, and forward the host's 8003 port to it.

This is a blocking command, so won't exit until Ctrl-C is pressed.

Now curl -v localhost:8003/hello.php should answer with 200 OK.

Do Docker containers have their own port space? What happens if while the first command is running, I start another identical one? What do I have to change to make them coexist?

7. Layer cache

Build a sample heavy image (taking more than 60 seconds to build) with docker build -f Dockerfile.heavy -t elifesciences/heavy .

Now change after.txt by adding a line or similar, and rebuild. What happens?

Change before.txt instead, and rebuild. What happens?

Run docker build -f Dockerfile.heavy -t elifesciences/heavy --no-cache . to skip the layer cache.