docker: storage and services

Docker Volume

Without going through Docker, accessing files within a Docker image is not easy. Therefore, Docker has a volume feature that allows users to specify the location on the host file system to serve as the access directory for Docker. In other words, a volume is the NFS of a Docker image.

Example: Using a volume to store SQLite files.

ref: 

SQLite for NodeJS: https://www.sqlitetutorial.net/sqlite-nodejs/

Initialize the project.

# Setup ExpressJS framework
express --view=pug 240324_ejs_sqlite_docker
npm init
npm install express
npm install sqlite3

Test:

npm start

Initialize docker 

Since the directory already contains NodeJS, the Docker Daemon will assist in the setup.

Create new docker image

docker build -t atfuture7/sqlite01 .

Create a folder for Docker, create a container, run it. 

  mkdir docker_vol
  docker run -p 3000:3000 -v ./docker_vol:/data --name exp_sqlite atfuture7/sqlite01

After confirming that the container can run correctly, stop the container and add content to the app.

Add sample project

This example chooses SQLite because SQLite is essentially just a file format and does not require any other application to run. It can be seen as a simple tool that only uses storage space and complies with the SQL language structure, making it well-suited for testing Docker's NFS.

Sample Web App:

sample code: https://github.com/atfuture7/testcode/tree/master/docker/02_docker_nfs

GitHub only contains all new and modified files. 

To make the new file runnable, it is necessary to install the module mod_story used for running SQLite.

npm install mod_story 

Rebuild Dock image and container

Operational: 

Since my PowerShell does not handle branches, commands are presented in the format I execute them.

  docker build -t atfuture7/sqlite01 .
  docker run  -p 3000:3000 -v ./docker_vol:/data --name exp_sqlite  atfuture7/sqlite01

After executing several additions at http://localhost:3000/idx2, the docker_vol/story.sqlite file can be seen in the execution directory.

* test/www is the entry point of the development environment, with the DB file set to (relative directory) ./docker_vol/story.sqlite.

* bin/www is the production environment, with the DB file set to (absolute directory) /data/story.sqlite.

Programmatic: 

Modify the compose.yaml file to add volume settings. By executing docker compose, the image and container can be built.

docker compose up --build

Docker services

The previous section is about creating your own image and the instructions for creating a container with compose.yaml. What the entry-point of a Docker image is, is determined by the Dockerfile settings. In other words, images pulled from the internet require developers to reveal the information needed to start the image. For complex control mechanisms, using compose would be easier.

Example: MySQL docker 

ref: 

https://www.datacamp.com/tutorial/set-up-and-configure-mysql-in-docker

https://hub.docker.com/_/mysql

Operational: 

docker run --name some-mysql -v ./docker_vol:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -p 3306:3306 -d mysql

Programmatic: 

gitHub: https://github.com/atfuture7/testcode/tree/master/docker/03_docker_mysql

We will discuss the case of compose including several services next time. The example below shows the space occupied by the DB image.