Redirect *.example.com to *.example.org with HAProxy

haproxy.cnf

# We use a temporary header to build our new Host header from the existing one
# and then directly perform a redirect

# Clean the request and remove any existing header named X-Rewrite
http-request del-header X-REWRITE

# Copy the Host header into X-Rewrite unchanged
http-request add-header X-REWRITE %[hdr(host)] if { hdr_end(host) .example.com }

# Change the X-REWRITE Header to contain out new host name
http-request replace-header X-REWRITE (.*)\.example\.com$ \1.example.org if { hdr_count(X-REWRITE) gt 0 }

# Perform the 301 redirect
http-request redirect code 301 location %[hdr(X-REWRITE)]%[req.uri] if { hdr_count(X-REWRITE) gt 0 }