How can I enable HTTP/2 on HAProxy?

Question

We have recently shifted from HTTP to HTTPS. As we have already moved to HTTPS, we are thinking of moving to HTTP/2 to get performance benefits.

As explained above that requests between browser and LB are secured (HTTPS) while communication between LB and app server still using HTTP

What is the possibility of enabling HTTP /2 with the current setup? Can we enable HTTP/2 between browser and LB while communication between LB and app servers remain on HTTP?

Answer 1

2017 update: HAProxy 1.8 supports HTTP/2

From the 1.8 announcement:

HAProxy 1.8 now supports HTTP/2 on the client side (in the frontend sections) and can act as a gateway between HTTP/2 clients and your HTTP/1.1 and HTTP/1.0 applications.

You'll need the h2 directive in your haproxy.conf. From CertSimple's HAProxy HTTP/2 and dynamic load balancing guide:

frontend myapp
  bind :443 ssl crt /path/to/cert.crt alpn h2,http/1.1
  mode http

Older versions of HAProxy

Older versions of HAProxy like 1.6 and 1.7 only support pass-through HTTP/2 - ie, directing traffic onto a seperate app server that supports HTTP/2. This is significantly more complicated - see other answers on how to do this. To terminate HTTP/2 and read the traffic on HAProxy, you'll need HAProxy 1.8.