You will need HAProxy 1.5 or later, because it provides support for SSL and ALPN, both required by HTTP/2. Most Linux distributions have the HAProxy package available to be installed out of the box. For example on Ubuntu 15.04:

$ sudo apt-get install haproxy

Alternatively you can download the HAProxy source code and build it on your environment by following the README bundled with the HAProxy source code tarball.

HAProxy will perform the TLS decryption and encryption much more efficiently than a Java implementation.

HAProxy will need a single file containing the X509 certificates and the private key, all in PEM format, with the following order:

Let’s use keytool to generate a self signed certificate:

$ keytool -genkeypair -keyalg RSA -keystore keystore.p12 -storetype pkcs12 -storepass storepwd -ext SAN=DNS:domain.com
What is your first and last name?
[Unknown]:  *.domain.com
What is the name of your organizational unit?
[Unknown]:  Unit
What is the name of your organization?
[Unknown]:  Domain
What is the name of your City or Locality?
[Unknown]:  Torino
What is the name of your State or Province?
[Unknown]:  TO
What is the two-letter country code for this unit?
[Unknown]:  IT
Is CN=*.domain.com, OU=Unit, O=Domain, L=Torino, ST=TO, C=IT correct?
[no]:  yes

The above command will generate a self signed certificate and private key for domain.com and subdomains, stored in the keystore.p12 file in PKCS#12 format. We need to extract the certificate and the private key in PEM format.

To extract the certificate into certificate.pem:

$ keytool -exportcert -keystore keystore.p12 -storetype pkcs12 -storepass storepwd -rfc -file certificate.pem

To export the private key into private_key.pem:

$ openssl pkcs12 -in keystore.p12 -nodes -nocerts -out private_key.pem -passin pass:storepwd

At this point you just need to concatenate the two files into one, in the correct order:

$ cat certificate.pem private_key.pem > domain.pem

The domain.pem file will be used later by HAProxy.

Now we can setup haproxy.cfg to configure HAProxy. This is a minimal configuration:

global
tune.ssl.default-dh-param 1024

defaults
timeout connect 10000ms
timeout client 60000ms
timeout server 60000ms

frontend fe_http
mode http
bind *:80
# Redirect to https
redirect scheme https code 301

frontend fe_https
mode tcp
bind *:443 ssl no-sslv3 crt domain.pem ciphers TLSv1.2 alpn h2,http/1.1
default_backend be_http

backend be_http
mode tcp
server domain 127.0.0.1:8282

The HAProxy configuration file works in the following way. The fe_http front-end accepts connections on port 80 and redirects them to use the https scheme.

The fe_https front-end accepts connections on port 443 and it is where the TLS decryption/encryption happens. You must specify the path to the PEM file containing the TLS key material (the crt domain.pem part), the ciphers that are suitable for HTTP/2 (the ciphers TLSv1.2), and the ALPN protocols supported (the alpn h2,http/1.1 ). This front-end then forwards the now decrypted bytes to the back-end in mode tcp. The mode tcp says that HAProxy will not try to interpret the bytes as HTTP/1.1 but instead opaquely forward them to the back-end.

The be_http back-end will forward (again in mode tcp) the clear-text bytes to a Jetty connector that talks clear-text HTTP/2 and HTTP/1.1 on port 8282.

The Jetty setup follows the steps of having Jetty installed in the JETTY_HOME directory, creating a JETTY_BASE directory and initializing it using Jetty’s command line tools. You must enable the http2c module, that is the module that speaks clear-text HTTP/2. Since the http2c module depends on the http module, the http module will be enabled transitively, and the final setup will therefore support both HTTP/2 and HTTP/1.1 in clear text.

Additionally, you will also enable the deploy module to be able to deploy a sample web application:

$ JETTY_BASE=haproxy-jetty-http2
$ mkdir $JETTY_BASE
$ cd $JETTY_BASE
$ java -jar $JETTY_HOME/start.jar --add-to-start=http2c,deploy

Now let’s deploy a demo web application and start Jetty:

$ cd $JETTY_BASE
$ cp $JETTY_HOME/demo-base/webapps/async-rest.war $JETTY_BASE/webapps/
$ java -jar $JETTY_HOME/start.jar jetty.http.host=127.0.0.1 jetty.http.port=8282

Now you can browse https://domain.com/async-rest (replace domain.com with your own domain, or with localhost, to make this example work).

Browsers supporting HTTP/2 will connect to HAProxy, which will decrypt the traffic and send it to Jetty. Likewise, HTTP/1.1 clients will connect to HAProxy, which will decrypt the traffic and send it to Jetty.

The Jetty connector, configured with the http2c module (and therefore transitively with the http module) is able to distinguish whether the incoming bytes are HTTP/2 or HTTP/1.1 and will handle the request accordingly.

The response is relayed back to HAProxy, which will encrypt it and send it back to the remote client.

This configuration offers you efficient TLS offloading, HTTP/2 support and transparent fallback to HTTP/1.1 for clients that don’t support HTTP/1.1.