Month: April 2020

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Configure HAproxy to load balance Centos httpd containers

In this article I will explain a HAproxy installation on docker centos images. First things first, 3 centos images should be deployed. Two of them will be simple web servers with httpd installed and the third one will have haproxy installed to load balance between the two web servers.

In order to deploy 3 new centos docker images you should first download the latest centos image.

Just pull the Centos docker image from dockerHub by using the below command

docker pull centos

And then deploy 3 instances of it:

docker container run -it --name centos-lab1 -d centos:latest
docker container run -it --name centos-lab2 -d centos:latest
docker container run -it --name centos-lab3 -d centos:latest

Verify that containers have been deployed succesfully and execute some interactive commands on them.

docker exec -it centos-lab1 uname -r

You will get a result like the below, depending on the image you have installed.

4.19.76-linuxkit

Install httpd package on the two web servers. I am using portainer so that I can interact easier with containers. You could also execute an interactive command as shown below.

yum install httpd
docker exec -it centos-lab2 yum install httpd

Lastly you should install haproxy package for the third server that will be used as a load balancer.

yum install haproxy
[root@ad1d23c22355 /]# haproxy -v
HA-Proxy version 1.8.15 2018/12/13
Copyright 2000-2018 Willy Tarreau

Verify connectivity between your containers. Based on the default network that have been deployed on my computer I get the following 3 IP’s.

172.17.0.4 , 172.17.0.5 , 172.17.0.6

Install a test html page on web servers that will be used to identify the node.

echo "this is centos-lab1" > /var/www/html/index.html
echo "this is centos-lab2" > /var/www/html/index.html

Enable and start httpd server on web servers and test that their page is up and running by running a curl from load balancer (server 3). You will get a respond like the below:

apache is running and responding on web servers 1,2

In order to use systemctl and systemd commands, check my previous article about deploying a Centos Image with systemd enabled.

Edit haproxy configuration setting under /etc/haproxy/haproxy.cfg and add your two webservers as backend servers of app section.

haproxy configuration

Restart haproxy so that configuration changes are loaded:

systemctl restart haproxy

Curl loadbalancer and verify from the results that load is balanced between centos-1 and centos-2 webservers:

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Deploy a CentOS container image with systemd enabled

In order to deploy a CentOS container with systemd enabled to perform and use commands as systemctl you could do the following:

Download the official Centos image with systemd integrated from DockerHub and create a file name Dockerfile on your current working directory. The following dockerfile will install/enable httpd package with yum and systemctl.

FROM centos/systemd
MAINTAINER "Your Name" you@example.com
RUN yum -y install httpd; yum clean all; systemctl enable httpd.service
EXPOSE 80
CMD ["/usr/sbin/init"]

Build your image:

docker build --rm --no-cache -t centos-sd-1 .

And then deploy a new container from your created image:

docker run --privileged --name centos-sd-1 -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 80:80 -d centos-sd-1

Verify that you can run successfully systemd commands:

[root@179a5c228835 /]# systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
Active: active (running) since Sun 2020-04-05 13:18:06 UTC; 9min ago
Docs: man:httpd(8)
man:apachectl(8)