CODEWITHSUNDEEP
docker
KEINOS
KEINOS

Reputation: 1224

In Docker, how do I detect from inside a container, that if a file or a directory is mounted by the Docker?

I did docker-compose down/docker container rm and noticed that I lost all my data created in the container. Yes, I forgot to mount my local directory as a volume in the first place. 😭

To prevent this, on startup, I want to warn users that "the data will be non-persistent", if the local volume's not mounted.

Is there a way to detect from inside container whether a file or a directory is a mounted one via Docker?

I googled it but couldn't find a good way. And my current workaround is:

FROM alpine:latest

RUN \
  mkdir /data && \
  touch /data/.replaceme
...

ENTRYPOINT /detect-mount-and-start.sh

detect-mount-and-start.sh checks if /data/.replaceme exists. If so, it warns to mount a local volume and exits.

Are there a better way to detect it?

Note (2019/09/12): This container is not only used via docker-compose up but docker run --rm too. And the directory name in local are not specified. Meaning, it can be -v $(pwd)/mydata:/data or something like -v $(pwd)/data_local:/data, etc.

Note (2019/09/15): The situation is: I launched a container of Markdown Editor and created something like 100 of .md files. Those files were saved on /data on the root of the container. I should have mounted the volume like -v $(pwd)/data:/data before everything. But I didn't ... and noticed it after removing the container. My bad I know.

Upvotes: 0

Views: 1904

Answers (3)

Datoon
Datoon

Reputation: 574

docker-compose stop - doesn't destroy your containers

Then you can use:

docker-compose start

Upvotes: 0

Joerison
Joerison

Reputation: 49

I don't know if I understand your question, but when you use docker-compose down, depending on how you create your docker-compose.yml, it will destroy your data, see:

Will delete you data when you execute down:

version: '2'
   mysqldb:
     image: mysql: 5.7

Don't will delete when you execute down:

version: '2'
   mysqldb:
     image: mysql: 5.7
     volumes:
       - ./data:/var/lib/mysql

Don't will delete when you execute down:

version: '2'
   mysqldb:
     image: mysql: 5.7
     volumes:
       - data-volume:/var/lib/mysql

volumes:
   data-volume:
     external: true

PS: I do not have a rating to comment on your question, so I am answering.

Upvotes: 2

Adiii
Adiii

Reputation: 59896

The way you are doing may also work, but I was working with one of my client on a project in development environment, It was nodejs based application and they need to make sure the server.js exist before starting the container and server.js was expected from mount location so I came up with this approach, As I did not find a way to sense shared docker volume inside container.

Dockerfile

FROM alpine
run mkdir -p /myapp
copy . /myapp
copy entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

entrypoint.sh

#!/bin/sh
APP_PATH="/myapp"
files=$(ls /myapp/*.js)
echo "Files in Docker mount location:  $files"
  if [ -f "$APP_PATH/server.js" ] && [ -f "$APP_PATH/index.js" ]; then
    echo "Starting container with host mount files"
    echo "Starting server.js"
    cd $APP_PATH;
    node server.js
  else
    >&2 echo "Error: Pls mount the host location on /myapp path of the container i.e -v host_node_project:/myapp. Current files $(ls $APP_PATH)"
    break
  fi

build and run

docker build -t myapp .
docker run -it --rm --name myapp myapp

enter image description here

Upvotes: 1

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