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--- howto:specific:learndocker [2025/01/15 13:22] – created alexdavis
+++ howto:specific:learndocker [2025/01/22 16:51] (current) – [Workshop tasks] alexdavis
@@ Line 1: / Line 1: @@
 ====== Learning Docker ======
-Placeholder
+This is a brief overview of using Docker, matching the contents of the 2025 Docker Workshop.
+==== What is Docker? ====
+Docker is a platform for containerising applications. This is like running applications in Virtual Machines (VMs), although with a smaller resource footprint and the advantage of being able to re-use base images to save setup.
+For most users Docker enables the rapid setting up of software, so if you do or are interested in self hosting then you should find this very useful.
+=== The Docker Workflow ===
+  - Start with an application
+  - Write a **Dockerfile** that replicates the setup needed for the application
+  - Use the **Docker Client** to build your application into an **image** using the **Dockerfile**
+  - Then use the **Client** again to run the **image** as a **container**
+  - Manage the running and configuration of multiple containers with **Docker Compose**
+=== Parts of the Docker architecture ===
+== Dockerfiles ==
+Dockerfiles are text files placed in the root of a project directory with instructions to build a **container**. They are comprised of **layers**, where each layer is modification to the image created by every layer "beneath" it. As such Dockerfiles normally start with a **Base Image** that provides a useful reusable starting point. Any image can be used as a base image, but normally they are things like particular OSes, or environments for a particular language or library (Python, Java, Node, etc). An example from the workshop is provided below:
+<file>
+FROM python:3.10-alpine
+# Install flask
+WORKDIR /code
+COPY requirements.txt /code
+RUN pip3 install -r requirements.txt
+# Copy the code to the image
+COPY . .
+# Open the flask port
+EXPOSE 5000
+CMD ["python", "FlaskApp/FlaskApp.py"]
+</file>
+Each line is a layer, and does the following:
+  - Loads the python 3.10 base image
+  - Moves into the /code directory
+  - Copies in the requirements file
+  - Installs the requirements
+  - Copies in the rest of the code
+  - Exposes the port the application uses
+  - Defines the command that runs when the container starts.
+== Images ==
+Images are built from Dockerfiles. They are immutable collections of binaries, config files, libraries and other files that are needed to run a particular application. Base images are uploaded to registries and can save a lot of work in creating your own images. This ranges from particular operating system environments to entire ready-to-configure applications.
+== Containers ==
+Containers are created from images. Containers are similar to virtual machines, but are not the same thing. They run applications in isolated, self-reliant environments. One of the advantages of Docker is that pretty much anywhere it runs, containers will run.
+== Compose ==
+Docker Compose is an extra tool for managing the running of multiple-container applications. It makes things like networking easier, as well as configuration by storing parameters manually passed to //docker run// in a configuration file (normally called //docker-compose.yml//). Note that Compose V1 is run with //docker-compose//, whereas V2 uses //docker compose//. Some systems will still use V1, but they function mostly the same, and identically for the sake of this guide.
+The //docker-compose.yml// file contains a list of services for the application, each of which has a defined configuration. All of these services can be brought up with a single command, which is handy. Below is an example of a compose file used in the workshop, although the extra networking configuration is specific to make it work on Sandbox.
+<file>
+version: "3.0"
+services:
+  flask:
+    image: localhost/myname/flaskapp
+    container_name: flask-compose
+    ports:
+      - YourPort:5000
+    environment:
+      - DISPLAY_NAME=YourName
+    networks:
+      - external
+# Below fixes a problem with Tardis container networking
+networks:
+  external:
+    name: podman
+    external: true
+</file>
+==== Workshop tasks ====
+Below is the interactive tasks from the workshop for people to work through at their own pace. Familiarity with Linux and Git is expected. [[https://git.tardisproject.uk/emily747/docker-workshop-2025|The workshop repo can be found here.]]
+=== Setup ===
+Sign up to Tardis if you haven't already and SSH into Sandbox.
+Clone the workshop repo:
+  git clone https://git.tardisproject.uk/emily747/docker-workshop-2025
+Look inside the Dockerfile, what does each layer do?
+=== Build an image ===
+Run the below in the same directory as the Dockerfile to build the image. Change "myname" to your name. The ":latest" tags the version of the image.
+<code>docker build -t myname/flaskapp:latest .</code>
+See the list of saved images with:
+<code>docker images</code>
+=== Run a  container ===
+Start your container with the following command, changing the display name argument and the port number. If the port number is in use run //docker rm flask// then try a different port.
+<code>
+docker run -e DISPLAY_NAME=YourName --name flask -p YourPort:5000 -d flaskapp
+</code>
+You can check if the container is working properly by making a request to the port it uses, by listing your running containers and by checking the logs of the container.
+<code>
+curl localhost:YourPort
+docker ps
+docker logs flask
+</code>
+Then stop and remove the container. Note that docker does not automatically remove stopped containers, you can see stopped containers with //docker ps -a//.
+<code>
+docker stop flask && docker rm flask
+</code>
+=== Configure your container with Compose ===
+Make sure your current container is stopped, then edit the //docker-compose.yml// file to have your name and port number. You can then start the container with Compose using:
+  docker-compose up -d
+The //-d// flag detaches the container output from your terminal window. Check the output from the container with //curl localhost:YourPort// as above. Then, modify the DisplayName environment variable in the compose file and bring the container down and up again.
+<code> docker-compose down && docker-compose up -d</code>
+Curl the port again - it should have changed. Stop your container again with //docker-compose down//.
+=== Extra tasks to look into ===
+  * Look into mounting and accessing a volume with Compose
+  * Open a shell in the container with //docker exec -it flask(-compose) sh//
+  * Try finding a docker image online and adding it as a service
+  * Find a piece of self-hosted software you can run as a Docker container