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Docker

Container Volume & Persistent Data

Containers are immutable (unchanged) and ephemeral (temporary).

2 ways for persistent data:

volume = special location outside of container, but inside docker folder

bind mount = link container path to host path (on same server)

NAME VOLUMES

# list all volume

docker volume ls

# check docker hub to get folder location

VOLUME [/var/lib/mysql]

# inspect and check 'Volumes' and 'Mounts' point

docker container inspect mysql

# source: real host path

# each container use different data folder, UNLESS we assign both to use 1 source

# this data live outside of containers, even if we remove containers (it's safe)

"Source": "var/lib/docker/volumes/xxxxxxxxxx/_data"

# destination: container path

VOLUME [/var/lib/mysql]

# set custom name for volume, instead of "xxxxxxxxxxx"

# assign both to use 1 source of named VOLUME

docker container run -d --name mysql1 -v mysql-data:/var/lib/mysql

docker container run -d --name mysql2 -v mysql-data:/var/lib/mysql

---

# create a new volume

docker volume create pspl

# check docker hub to get folder location

VOLUME [/var/lib/postgres/data]

# map old postgres version to pspl volume

docker container run -d --name pspl1 -v pspl:/var/lib/postgres/data postgres:9.1

# check log and stop old container

docker container stop pspl1

# map new container to pspl volume

docker container run -d --name pspl2 -v pspl:/var/lib/postgres/data postgres:9.2

SHOULD CREATE VOLUME IN DOCKERFILE

BIND MOUNT

edit file in macOS (host), see changes in Docker (container)

Can’t use in Dockerfile BUT is great for developer testing

# this shows how we can extend/change an existing official image from Docker Hub

FROM nginx:stable-alpine

# highly recommend you always pin versions for anything beyond dev/learn

WORKDIR /usr/share/nginx/html

# change working directory to root of nginx webhost

# using WORKDIR is preferred to using 'RUN cd /some/path'

COPY index.html index.html

# I don't have to specify EXPOSE or CMD because they're in my FROM

# when we run this in our current code folder /dockerfile-sample-2

docker container run -d --name nginx -p 80:80 -v $(pwd):/usr/share/nginx/html nginx

# we map the host / current working folder --> the container folder

# if we change files in code folder, nginx will show latest files

# same build, but only files inside that container

# can't develop further

docker container run -d --name nginx -p 80:80 nginx

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