Lab 19: The ‘Exec’ Command

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In this lab we are going to look into docker-compose exec command. Docker exec is used to run commands in a running container, similarly docker-compose exec runs commands in your services.

Command instructions

Exec

docker-compose exec [options] [-e key=val...] service command [args...]

Run commands in your services. Commands are by default allocating a TTY.

Options include:
-T disables pseudo-tty allocation.
--index=index specifies container when there are multiple instances of a service

Tested Infrastructure

Platform	Number of Instance	Reading Time
Play with Docker	1	5 min

Pre-requisite

Create an account with DockerHub
Open PWD Platform on your browser
Click on Add New Instance on the left side of the screen to bring up Alpine OS instance on the right side

Setup enviroment

$ mkdir app
$ cd app

Create a docker-compose.yml file

version: '3.1'
services:
  #Webservers
   webserver:
     image: nginx:alpine
     restart: unless-stopped
     expose:
       - "80"
       - "443"
  #Load Balancer
   loadbalancer:
     image: nginx:alpine
     volumes:
       - ./nginx.conf:/etc/nginx/nginx.conf:ro
     depends_on:
       - webserver
     ports:
       - "80:4000"

Create a nginx.conf file

user  nginx;
events {
    worker_connections   1024;
}
http {
        server {
              listen 4000;
              location / {
                proxy_pass http://webserver:80;
              }
        }
}

Note: This file will configure our load balancer.

Create the compose containers

$ docker-compose up -d --scale webserver=3

View the containers

$ docker-compose ps

Execute commands in different webservers

$ docker-compose exec --index=1 webserver  sh -c "echo 'Welcome to webserver1' > /usr/share/nginx/html/index.html"
$ docker-compose exec --index=2 webserver  sh -c "echo 'This is webserver2' > /usr/share/nginx/html/index.html"
$ docker-compose exec --index=3 webserver  sh -c "echo 'Webserver3 is up' > /usr/share/nginx/html/index.html"

Verify changes

$ curl http://localhost

Note: In order to verify all changes we’ll have to use the curl command multiple times.

Lab 19: The ‘Exec’ Command

Command instructions

Exec

Tested Infrastructure

Pre-requisite

Setup enviroment

Create a docker-compose.yml file

Create a nginx.conf file

Create the compose containers

View the containers

Execute commands in different webservers

Verify changes

Lab 19: The ‘Exec’ Command

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