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Manage Docker Containers Volume and Environment

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Docker volume is a way to store and manage persistent data in Docker containers. A Docker volume is a directory on the host system that is mounted into a container. Data stored in a Docker volume persists even after the container is deleted. Docker volumes are useful for storing data that needs to be shared between multiple containers, such as databases or configuration files.

Volume

Creating a volume

docker container run --name demo \
    alpine /bin/sh -c 'echo "This is a test" > sample.txt'

docker container diff demo

docker volume create sample
docker volume inspect sample
[
    {
        "CreatedAt": "2021-09-23T14:46:59Z",
        "Driver": "local",
        "Labels": {},
        "Mountpoint": "/var/lib/docker/volumes/sample/_data",
        "Name": "sample",
        "Options": {},
        "Scope": "local"
    }
]

Mounting a volume

docker container run --name test -it \
    -v sample:/data \
    alpine /bin/sh

cd /data / && echo "hello world" > data.txt && exit

ls /var/lib/docker/volumes/sample/_data

Removing volumes

docker volume rm sample

## emove all running containers
docker container rm -f $(docker container ls -aq)

Sharing data between containers

docker container run -it --name writer \
    -v shared-data:/data \
    alpine /bin/sh

docker container run -it --name reader \
    -v shared-data:/app/data:ro \
    ubuntu:18.04 /bin/bash

Using host volumes

mkdir /opt/src
docker container run --rm -it \
    -v /opt/src:/app/src \
    alpine:latest /bin/sh

Defining volumes in images

VOLUME /app/data
VOLUME /app/data, /app/profiles, /app/config
VOLUME ["/app/data", "/app/profiles", "/app/config"]

Env

Defining environment variables for containers

docker container run --rm -it \
    --env LOG_DIR=/var/log/my-log \
    alpine /bin/sh
export && exit

env.conf

LOG_DIR=/var/log/my-log
MAX_LOG_FILES=5
MAX_LOG_SIZE=1G
docker container run --rm -it \
    --env-file ./env.conf \
    alpine sh -c "export"

Defining environment variables in container images

Dockerfile

FROM alpine:latest
ENV LOG_DIR=/var/log/my-log
ENV  MAX_LOG_FILES=5
ENV MAX_LOG_SIZE=1G
docker image build -t my-alpine .
docker container run --rm -it \
    my-alpine sh -c "export | grep LOG"

Environment variables at build time

Dockerfile

ARG BASE_IMAGE_VERSION=12.7-stretch FROM node:${BASE_IMAGE_VERSION} WORKDIR /app
COPY packages.json .
RUN npm install
COPY . .
CMD npm start
docker image build \
    --build-arg BASE_IMAGE_VERSION=12.7-alpine \
    -t my-node-app-test .
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