Lab #19: Exec Command
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.