Do you need to create HA proxy and thinking of Nginx ? Or maybe thinking even further … about Nginx and docker ? So something really simple and what you can defenitely take to next level.

In my scenario I need something which you could call … hmmm a “service gateway” ?! Which i a nutshell is solution which exposes HA loadbalancer ( and in future also DNS with connection to Consul ).

Raw and basic design could look as follow :

So what we have here are 2 hosts that will expose a VIP address. So nothing really edge cutting right 😀 And as recently I work a lot with Ubuntu following steps are geared towards that OS.

Installing:

installation is really plain simple. You can use APT to get package installed by running:

apt-get update && apt-get install keepalived

 

And thats it for installation part 🙂 nothing like quick install 🙂

 

Configuring:

Configuration is something on which you can spend some more time tuning it to your needs. It does have a lot of options and I recommend just do a bit of reading. I will highlight here only bare metal basics to get you running. But complex scenarios are well possible.

Also you will notice that I do not use multicasting but switched to unicast

 

First thing which you want to configure is binding settings ( otherwise we want to be able to get solution running )

echo "net.ipv4.ip_nonlocal_bind=1" >> /etc/sysctl.conf
sysctl -p

 

Next we create configuration file for our service

vi /etc/init/keepalived.conf

 

and once thats done you can paste contents of the snipet below

description "lb and ha service"

start on runlevel [2345]
stop on runlevel [!2345]

respawn

exec /usr/local/sbin/keepalived --dont-fork

 

Once done  we create config file /etc/keepalived/keepalived.conf ( on our first node )

vrrp_instance VI_1 {
        interface eth0
        state MASTER
        virtual_router_id 91
        priority 100
        virtual_ipaddress {
            # YOUR VIP ADDRESS # 
        }
        unicast_src_ip #YOUR-1st-NODE-ADDRESS
        unicast_peer {
         #YOUR-2nd-NODE-ADDRESS
        }
}

 

And on the other machine you place the same config but switch addresses in unicast source and peer

vrrp_instance VI_1 {
        interface eth0
        state MASTER
        virtual_router_id 91
        priority 100
        virtual_ipaddress {
            # YOUR VIP ADDRESS # 
        }
        unicast_src_ip #YOUR-2nd-NODE-ADDRESS
        unicast_peer {
         #YOUR-1st-NODE-ADDRESS
        }
}

 

More details on configuration you can find here >>>  http://www.keepalived.org/LVS-NAT-Keepalived-HOWTO.html ( I have found this link to be full of useful information )

 

Bringing service to live:

Now you might say that I have configured both as masters. But in this case first one to be online will become master.

Now on both nodes you can execute

# Start service
service keepalived start
# show ip addresses
ip addr show eth0

And on one you should see your VIP address being online. voilla! HA service running and operational

 

Testing Nginx:

Now time has come to test nginx. for purposes of this demo I have setup both machines to host docker container of nginx

 

Great! So both are listening on correct VIP address. One is displaying message “Hello from Nginx-1” and second “Hello from Nginx-2”. Lets test that from client machine …

Initial request from our client machine :

 

And let me know disable network interface on host-1 and once thats done we make request again

 

 

The error you see here is kinda my fault (but wanted to highlight this ) since my keepaliveD service was stopped on the host. once I started the service it responded from the other host.

 

Summary:

So now whats ur options ? Well quite a lot – as you can i.e. setup glusterFS and replicate your nginx config files / or use consul – explore consul template and use that for nginx dynamic files …

If you have any interesting use case scenarios leave them in comments!