What is HAProxy and Keepalived?

What is HAProxy and Keepalived?

HAProxy (High Availability Proxy) is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications. Instagram, Dropbox, and Medium are some of the popular companies that use HAProxy, whereas Keepalived is used by Gini, Groupe La Poste, and utry.

What does Keepalived do?

Keepalived is a piece of software which can be used to achieve high availability by assigning two or more nodes a virtual IP and monitoring those nodes, failing over when one goes down. Keepalived can do more, like load balancing and monitoring, but this tutorial focusses on a very simple setup, just IP failover.

Does DNS use round robin?

A DNS server with round-robin enabled will have multiple different A records, each with the same domain name but a different IP address. Each time the DNS server is queried, it sends the IP address to which it most recently responded with to the back of the queue, operating on a loop.

What port does Keepalived use?

Keepalived will now use VRRP to elect an active node, which in turn will listen on the virtual_server IP and port, in this case the VRRP virtual IP and TCP port 25.

What happens if HAProxy goes down?

If the primary load balancer goes down, the floating IP will be moved to the second load balancer automatically, allowing service to resume.

What are some of the disadvantages of a round robin DNS?

Although easy to implement, round-robin DNS has a number of drawbacks, such as those arising from record caching in the DNS hierarchy itself, as well as client-side address caching and reuse, the combination of which can be difficult to manage. Round-robin DNS should not solely be relied upon for service availability.

How do I configure Keepalived?

How to Setup IP Failover with KeepAlived on Ubuntu & Debian

1. Step 1 – Install Required Packages.
2. Step 2 – Install Keepalived.
3. Step 3 – Setup Keepalived on LB1.
4. Step 4 – Setup KeepAlived on LB2.
5. Step 5 – Start KeepAlived Service.
6. Step 6 – Check Virtual IPs.
7. Step 7 – Verify IP Failover Setup.