docker copy file from one container to another? - docker

Question

Here is what I want to do:
docker-compose build
docker-compose $COMPOSE_ARGS run --rm task1
docker-compose $COMPOSE_ARGS run --rm task2
docker-compose $COMPOSE_ARGS run --rm combine-both-task2
docker-compose $COMPOSE_ARGS run --rm selenium-test
And a docker-compose.yml that looks like this:
task1:
build: ./task1
volumes_from:
- task1_output
command: ./task1.sh
task1_output:
image: alpine:3.3
volumes:
- /root/app/dist
command: /bin/sh
# essentially I want to copy task1 output into task2 because they each use different images and use different tech stacks...
task2:
build: ../task2
volumes_from:
- task2_output
- task1_output:ro
command: /bin/bash -cx "mkdir -p task1 && cp -R /root/app/dist/* ."
So now all the required files are in task2 container... how would I start up a web server and expose a port with the content in task2?
I am stuck here... how do I access the stuff from task2_output in my combine-tasks/Dockerfile:
combine-both-task2:
build: ../combine-tasks
volumes_from:
- task2_output

Answer 1

In recent versions of docker, named volumes replace data containers as the easy way to share data between containers.
docker volume create --name myshare
docker run -v myshare:/shared task1
docker run -v myshare:/shared -p 8080:8080 task2
...
Those commands will set up one local volume, and the -v myshare:/shared argument will make that share available as the folder /shared inside each of each container.
To express that in a compose file:
version: '2'
services:
task1:
build: ./task1
volumes:
- 'myshare:/shared'
task2:
build: ./task2
ports:
- '8080:8080'
volumes:
- 'myshare:/shared'
volumes:
myshare:
driver: local
To test this out, I made a small project:
- docker-compose.yml (above)
- task1/Dockerfile
- task1/app.py
- task2/Dockerfile
I used node's http-server as task2/Dockerfile:
FROM node
RUN npm install -g http-server
WORKDIR /shared
CMD http-server
and task1/Dockerfile used python:alpine, to show two different stacks writing and reading.
FROM python:alpine
WORKDIR /app
COPY . .
CMD python app.py
here's task1/app.py
import time
count = 0
while True:
fname = '/shared/{}.txt'.format(count)
with open(fname, 'w') as f:
f.write('content {}'.format(count))
count = count + 1
time.sleep(10)
Take those four files, and run them via docker compose up in the directory with docker-compose.yml - then visit $DOCKER_HOST:8080 to see a steadily updated list of files.
Also, I'm using docker version 1.12.0 and compose version 1.8.0 but this should work for a few versions back.
And be sure to check out the docker docs for details I've probably missed here:
https://docs.docker.com/engine/tutorials/dockervolumes/

Answer 2

For me the best way to copy file from or to container is using docker cp for example:
If you want copy schema.xml from apacheNutch container to solr container then:
docker cp apacheNutch:/root/nutch/conf/schema.xml /tmp/schema.xml
server/solr/configsets/nutch/
docker cp /tmp/schema.xml
solr:/opt/solr-8.1.1/server/solr/configsets/nutch/conf