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98 lines
3.0 KiB
98 lines
3.0 KiB
2 years ago
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# Lesson 2: Introduction to Docker image builds
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1. Clone this git repository.
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1. Change directory into `lesson02`:
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$ cd lesson02
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1. Why are containers useful? What are their advantages over a
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traditional server?
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- containers are light
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- containers are portable
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- containers are isolated
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- containers can be run "immutably"
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- containers are built hierarchically
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- developers can create applications without a full server-stack
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1. What are some limitations of containers?
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- interaction is more difficult for multiple containers than for
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multiple server process (although Kubernetes helps)
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- some overhead so not quite as fast as "bare-metal" processes
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- there are several decades worth of server administration best practices
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and tools but only a few years for containers
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- not good for large tightly-integrated applications (e.g., Oracle database)
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1. Question: what is the difference between an "image" and a "container"?
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(See also [this Stackoverflow
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question](https://stackoverflow.com/questions/23735149/what-is-the-difference-between-a-docker-image-and-a-container)).
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1. Most Docker images are build on top of existing "base" images. These
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base containers are usually hosted in Docker Hub. For example, all Debian
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releases come as Docker images; see https://hub.docker.com/_/debian for a
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list of the base Debian Docker images.
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1. Let's build a "Hello, world." Docker image. We will build it on a
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Debian buster base. First, pull the Docker image:
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$ docker pull debian:buster-slim
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# We pull the "slim" image to save disk space
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1. Here is an application that echos "Hello, world." and then exits (this
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file is also in the current directory).
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#!/bin/sh
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echo "Hello, world."
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exit 0
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1. Now we create a "Dockerfile" that tells the build process how to create
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the image. We use `debian:buster-slim` as the base and "add" the command
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`run.sh`. The first argument of `ADD` is the *local* copy of the file and
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the second argument is where we want the file to be in the image.
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# Dockerfile
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FROM debian:buster-slim
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LABEL maintainer="adamhl@stanford.edu"
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ADD run.sh /root/run.sh
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1. We want to make sure that the script will run, so make it executable.
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# Dockerfile
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FROM debian:buster-slim
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LABEL maintainer="adamhl@stanford.edu"
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ADD run.sh /root/run.sh
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RUN chmod a+x /root/run.sh
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1. Docker containers must be told which command to run. We do this with
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the `CMD` directive
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# Dockerfile
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FROM debian:buster-slim
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LABEL maintainer="adamhl@stanford.edu"
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ADD run.sh /root/run.sh
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RUN chmod a+x /root/run.sh
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CMD /root/run.sh
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1. We are now ready to build the image:
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$ docker build . -t hello-world
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$ docker images | grep hello-world
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1. Question: what is the purpose of `.` (dot) in the above `docker build`
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command?
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1. Note that the tag is `latest` (the default).
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1. Let's run this image in a container:
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$ docker run --rm hello-world
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1. Did you see what you expected?
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