Posts Tagged - docker

Data generated and used by Docker containers does not persist after restarts. We use Docker volumes to manage data to solve this issue. We use it to persist data in a container or share data between containers.

Volumes are the preferred mechanism for persisting data generated and user by Docker containers. Volumes are easier to back up or migrate.

Volumes are often a better choice than persisting data in a container’s writable layer, because a volume does not increase the size of the containers using it. The volume’s contents exist outside the lifecycle of a given container.

We have 3 volume types:

Anonymous volumes

Helpful to persist data temporarily. If we restart our container data is still visible. It doesn’t persist when we remove the container. Not accessible by other containers. They’re created inside /var/lib/docker/volume.

Example file:

version: '3.8'  
services:  
  db:  
    image: mysql  
    restart: always  
    environment:  
      MYSQL_ROOT_PASSWORD: root  
      MYSQL_DATABASE: test_db  
    ports:  
      - "3306:3306"  
    volumes:  
      - /var/lib/mysql

Read More

Steps to go from a docker-compose file, to build an Image out of the file, upload it to DockerHub, and run it with Kubernetes (minikube).

Set up

Install Kompose

# linux
curl -L https://github.com/kubernetes/kompose/releases/download/v1.22.0/kompose-linux-amd64 -o kompose
chmod +x kompose
sudo mv ./kompose /usr/local/bin/kompose

Clone App and Host It into DockerHub

Clone the files, go to the directory where your Dockerfile is and run:

# mariocodes is my DockerHub username
# kubernetes-custom-java-maven-app is the name of the repo I created at DockerHub
docker build -f Dockerfile -t mariocodes/kubernetes-custom-java-maven-app .

Read More

List of things to do, to improve your Docker experience

Never map the public port on a DockerFile

If you map it, you’ll only be able to have one instance of this container running. If the user wants to map the port, he’ll be able to do it in a compose script or with -p option.

# public and private mapping
EXPOSE 80:8080 # don't do this

# private mapping
EXPOSE 80

Read More

TODO: Working docker-compose and DockerFile examples to complement this information Interesting tool to analyze custom Image layers size

Basic Definitions

Image Executable package that includes everything needed to run an application. It consists of read-only layers, each of which represent a DockerFile instruction. The layers are stacked and each one is a delta of changes from the previous layer.
Container Instance of an image.

Stack Defines the interaction of all the services
Services Image for a microservice which defines how containers behave in production

DockerFile File with instructions that allows us to build upon an already existing image. It defines:

• the base image to build from
• our own files to use or append
• the commands to run

At the end, a DockerFile will form a service, which we may call from docker-compose or standalone with docker build.

DockerFiles vs docker-compose A DockerFile is used when managing a single individual container. docker-compose is used to manage an application, which may be formed by one or more DockerFiles. Docker-compose may also be used as support to input large customization options, which otherwise would be parameters in a really long command.

You can do everything docker-compose does with just docker commands and a lot of shell scripting

Read More