HAPROXY: Redirect all requests to a URL starting with /foo to /bar while retaining everything following it

haproxy_1_5.cnf

# In HAProxy 1.5, we have to jump through some hops to accomplish a rewrite of a request's path...
# We use a temporary header to build our new path from the existing one in the request
# 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 full request URL into X-Rewrite unchanged
http-request add-header X-REWRITE %[url] if { path_beg /foo }

# Change the X-REWRITE header to contain out new path
http-request replace-header X-REWRITE ^/foo(/.*)?$ /bar\1 if { hdr_cnt(X-REWRITE) gt 0 }

# Perform the 301 redirect
http-request redirect code 301 location http://%[hdr(host)]%[hdr(X-REWRITE)] if { hdr_cnt(X-REWRITE) gt 0 }

haproxy_1_6.cnf

# In HAProxy 1.6, there is the regsub filter we can use here
http-request redirect code 301 location http://%[hdr(host)]%[url,regsub(^/foo,/bar,)] if { path_beg /foo }