more work on lesson2

lesson02/Dockerfile

+# Dockerfile
+FROM debian:buster-slim
+LABEL maintainer="adamhl@stanford.edu"
+
+ADD run.sh /root/run.sh
+RUN chmod a+x /root/run.sh
+CMD /root/run.sh

lesson02/README.md

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

lesson02/run.sh

+#!/bin/sh
+echo "Hello, world."
+exit 0