Add docker-compose file to run Minio in distributed mode (#2606)

Serves as a starting point to run a Minio cluster using Docker. The
file can be used as configuration for the docker-compose tool to start
4 Minio servers in distributed mode.

* Add a docker-compose.yml file to run 4 minio server instances in
  distributed mode

* Update Docker.md with command to use the file

docker-compose.yml

@@ -0,0 +1,46 @@
+version: '2'
+
+# starts 4 docker containers running minio server instances. Each
+# minio server's web interface will be accessible on the host at port
+# 9001 through 9004.
+services:
+  minio1:
+    image: minio/minio
+    ports:
+      - "9001:9000"
+    volumes:
+      - /mnt/export/minio1:/export
+    environment:
+      MINIO_ACCESS_KEY: abcd1
+      MINIO_SECRET_KEY: abcd1234
+    command: minio1:/export minio2:/export minio3:/export minio4:/export
+  minio2:
+    image: minio/minio
+    ports:
+      - "9002:9000"
+    volumes:
+      - /mnt/export/minio2:/export
+    environment:
+      MINIO_ACCESS_KEY: abcd1
+      MINIO_SECRET_KEY: abcd1234
+    command: minio1:/export minio2:/export minio3:/export minio4:/export
+  minio3:
+    image: minio/minio
+    ports:
+      - "9003:9000"
+    volumes:
+      - /mnt/export/minio3:/export
+    environment:
+      MINIO_ACCESS_KEY: abcd1
+      MINIO_SECRET_KEY: abcd1234
+    command: minio1:/export minio2:/export minio3:/export minio4:/export
+  minio4:
+    image: minio/minio
+    ports:
+      - "9004:9000"
+    volumes:
+      - /mnt/export/minio4:/export
+    environment:
+      MINIO_ACCESS_KEY: abcd1
+      MINIO_SECRET_KEY: abcd1234
+    command: minio1:/export minio2:/export minio3:/export minio4:/export

docs/Docker.md

@@ -12,7 +12,7 @@ docker run -p 9000:9000 minio/minio /export
 
 ## 2. Run One Minio Docker Container
 
-Minio container requires a persistent volume to store configuration and application data. Following command maps local persistent directories from the host OS to virtual config `~/.minio` and export `/export` directories. 
+Minio container requires a persistent volume to store configuration and application data. Following command maps local persistent directories from the host OS to virtual config `~/.minio` and export `/export` directories.
 
 ```sh
 
@@ -40,29 +40,14 @@ docker run -p 9000:9000 --name minio1 \
 
 ## 4. Run Minio in clustered mode
 
-Let's consider that we need to run 4 minio servers inside different docker instances.
+Let's consider that we need to run 4 minio servers inside different docker containers. The `docker-compose.yml` file in the root of the project sets this up using the [docker-compose](https://docs.docker.com/compose/) tool.
 
-### Prepare and start Minio docker instances
-```sh
-$ docker run -d --name=minio1 -e "MINIO_ACCESS_KEY=abcde" -e "MINIO_SECRET_KEY=secret00" -it -v/mnt/export/minio1:/export minio/minio
-$ docker run -d --name=minio2 -e "MINIO_ACCESS_KEY=abcde" -e "MINIO_SECRET_KEY=secret00" -it -v/mnt/export/minio2:/export minio/minio
-$ docker run -d --name=minio3 -e "MINIO_ACCESS_KEY=abcde" -e "MINIO_SECRET_KEY=secret00" -it -v/mnt/export/minio3:/export minio/minio
-$ docker run -d --name=minio4 -e "MINIO_ACCESS_KEY=abcde" -e "MINIO_SECRET_KEY=secret00" -it -v/mnt/export/minio4:/export minio/minio
-```
+### Start Minio docker instances
 
-### Get docker instances IP addresses:
-```sh
-$ docker ps -q | xargs -n 1 docker inspect  --format '{{ .NetworkSettings.IPAddress }}'
-172.17.0.2
-172.17.0.3
-172.17.0.4
-172.17.0.5
-```
+From the root directory of the project, run:
 
-### Run all minio instances
-```sh
-$ docker exec -d minio1 minio server 172.17.0.2:/export 172.17.0.3:/export 172.17.0.4:/export 172.17.0.5:/export
-$ docker exec -d minio2 minio server 172.17.0.2:/export 172.17.0.3:/export 172.17.0.4:/export 172.17.0.5:/export
-$ docker exec -d minio3 minio server 172.17.0.2:/export 172.17.0.3:/export 172.17.0.4:/export 172.17.0.5:/export
-$ docker exec -d minio4 minio server 172.17.0.2:/export 172.17.0.3:/export 172.17.0.4:/export 172.17.0.5:/export
+``` shell
+$ docker-compose up
 ```
+
+Each instance's minio web-server is accessible on the host at ports 9001 through 9004, so you may access the first one at http://localhost:9001/