You can use Docker in Docker (docker:dind image) to run multiple instances of Docker daemon on the same host, and have each tester use a different DOCKER_HOST to run their Compose stack. Each app instance will be deployed on a separate Docker daemon and isolated without requiring any change in docker-compose.yml.
Docker in Docker can be used to run a Docker daemon from another Docker daemon. (Docker daemon is the process actually managing your container when using docker). See Docker architecture and DinD original blogpost for details.
Example: run 2 Docker daemons exposing the app port
Let's Consider 2 testers with this docker-compose.yml:
version: 3
services:
app:
image: my/app:latest
ports:
- 8080:80
- Run 2 instances of Docker Daemon exposing Daemon port and any port that will be exposed by Docker Compose (see below why)
# Run docker dind and map port 23751 on localhost
# Expose Daemon 8080 on 8081 (port that will be used by Tester1)
# privileged is required to run dind (see dind-rootless exists but is experimental)
# DOCKER_TLS_CERTDIR="" is to deploy an unsecure Daemon
# it's easier to use but should only be used for testing/dev purposes
docker run -d \
-p 23751:2375 \
-p 8081:8080 \
--privileged \
--name dockerd-tester1 \
-e DOCKER_TLS_CERTDIR=""
docker:dind
# Second Daemon using port 23752
docker run -d \
-p 23752:2375 \
-p 8082:8080 \
--privileged \
--name dockerd-tester2 \
-e DOCKER_TLS_CERTDIR=""
docker:dind
- Each tester can run their own stack on their Docker daemon by setting
DOCKER_HOST env var:
# Tester 1 shell
# use dockerd-tester1 daemon on port 23751
export DOCKER_HOST=tcp://localhost:23751
# run our stack
docker-compose up -d
Same for Tester 2 on dockerd-tester2 port:
# Tester 2 shell
export DOCKER_HOST=tcp://localhost:23752
docker-compose up -d
- Interacting with Tester 1 and 2's stacks
Need the ability to build and run tests using our docker-compose files and need the ability to run the actual project on different ports
The exposed ports for each testers will be exposed on the Docker daemon host and reachable via http://$DOCKER_HOST:$APP_PORT instead of localhost:$APP_PORT (that's why we also exposed app port on each Daemon).
Considering our docker-compose.yml, testers will be able to access application such as:
# Tester 1
# port 8081 is linked to port 8080 of Docker daemon running our app container
# itself redirect on port 8080
# in short: 8081 -> 8080 -> 80
curl localhost:8081
# Tester 2
# 8082 -> 8080 -> 80
curl localhost:8082
Our deployment will look like this
Alternative without exposing ports, using Docker daemon IP directly
Similar to the first example, you can also interact with the deployed app by using Docker daemon IP directly:
# Run daemon without exposing ports
docker run -d \
--privileged \
--name dockerd-tester1 \
-e DOCKER_TLS_CERTDIR=""
docker:dind
# Retrieve daemon IP
docker inspect --format '{{ .NetworkSettings.IPAddress }}' dockerd-tester1
# output like 172.17.0.2
# use it!
export DOCKER_HOST=172.17.0.2
docker-compose up -d
# our app port are exposed on Daemon
curl 172.17.0.2:8080
We contacted directly our Daemon via its IP instead of exposing its port on localhost.
You can even define your Docker daemons with static IPs in a docker-compose.yml such as:
version: "3"
services:
dockerd-tester1:
image: docker:dind
privileged: true
environment:
DOCKER_TLS_CERTDIR: ""
networks:
dind-net:
# static IP to set as DOCKER_HOST
ipv4_address: 10.5.0.6
# same for dockerd-tester2
# ...
networks:
dind-net:
driver: bridge
ipam:
config:
- subnet: 10.5.0.0/16
And then
export DOCKER_HOST=10.5.0.6
# ...
Notes:
- This may have some performance impact depending on the machine on which Daemons are deployed
- You can use
dind-rootless instead of dind to avoid using --privileged flags
- It's better to avoid
DOCKER_TLS_CERTDIR: "" for security reasons, see TLS instruction on docker image for detailed usage of TLS
