HA Proxy support for HTTP/2 backend servers in http mode

Question

I have a tomcat 9.0.2 server supporting HTTP/2 and running on TLS1.2. Below is the connector configuration in server.xml

<Connector port="8443" protocol="org.apache.coyote.http11.Http11Nio2Protocol"
    address="0.0.0.0"
    maxThreads="150" SSLEnabled="true" asyncTimeout="10000" maxHeaderCount="50"
    maxPostSize="1048576" scheme="https" secure="true" compression="force" 
    compressionMinSize="2048" maxConnections="10000">
    <UpgradeProtocol className="org.apache.coyote.http2.Http2Protocol" />
    <SSLHostConfig protocols="TLSv1.2">
        <Certificate certificateKeystoreFile="${keystore.file.path}"
            certificateKeystorePassword="${keystore.password}"
            certificateKeyAlias="${server.cert.alias}"
            certificateKeystoreType="${keystore.type}" />
    </SSLHostConfig>
</Connector>

I am using HA Proxy 1.8 and configuration is like below

frontend  mydomain-ux
  mode    http
  bind    <ip>:8080 ssl crt /etc/certs/mydomain.com.cert.pem
  http-request set-var(txn.path) path
  acl mydomain hdr_end(host) -i mydomain.com
  use_backend mydomain_server if mydomain  

backend  mydomain_server
  mode    http
  server  mydomain_backeend_server <server-ip>:8443 ssl

Since, I have multiple backends based on host, I cannot use TCP mode and do pass through HTTP/2 SSL termination

Is there a way I can have HTTP/2 termination in backend mode http ?

Answer 1

As far as I'm aware HAProxy does not support HTTP/2 on the back end. They only recently announced front end support. (Edit 18th Jan 2019 - since added in v1.9 - https://www.haproxy.com/blog/haproxy-1-9-has-arrived/).

Even without backend HTTP/2 support, it is possible to terminate the front end on HTTPS, and then forward to the back end on TCP (without HTTPS), and it may be possible to use the SNI part of the HTTPS to do the optional routing you want (this is completely untested btw):

frontend  mydomain-ux
  mode    tcp
  bind    <ip>:8080 ssl crt /etc/certs/mydomain.com.cert.pem alpn h2,http/1.1
  use_backend     mydomain_server      if { ssl_fc_sni mydomain.com}
  use_backend     mydomain_server2     if { ssl_fc_sni mydomain2.com }
  default_backend mydomain_server

backend  mydomain_server
  mode    tcp
  server  mydomain_backeend_server <server-ip>:8081

This would allow your backend to speak HTTP/2 on port 8081 but without HTTPS (port 8443), and even works on HAProxy before 1.8 (when front end HTTP/2 support was added). However it would mean your Tomcat would need to be setup without SSL.

HAProxy also do not recommend using the SNI host for routing as discussed in this answer and in the the mailing thread it refers to. Plus additionally SNI support is not universal (though to all practical intents it is unless supporting really old browsers like IE8 on XP).

The other question you should ask yourself is if you really need HTTP/2 in the backend or if just supporting this at the HAProxy level is enough?