--- a/ansible/roles/hg-web/templates/vhost.conf.j2
+++ b/ansible/roles/hg-web/templates/vhost.conf.j2
@@ -6,16 +6,35 @@ WSGIPythonHome /var/hg/venv_hgweb
 # Default is 100. Mercurial encodes some arguments in HTTP request headers.
 # Repos with large numbers of heads (namely Try) run into these limits.
 LimitRequestFields 1000
 
 <VirtualHost *:80>
     ServerName hg.mozilla.org
     DocumentRoot /repo_local/mozilla/webroot_wsgi
 
+    # Clients processing e.g. bundle data may consume data much slower than the
+    # server can emit. This can result in the network being idle for >60s.
+    # Compounding this problem is that the load balancer has its own buffer.
+    # So there may be network activity between the client and the load balancer
+    # but not between the load balancer and this server. That can lead to even
+    # longer periods of network idle. We increase the timeout from its default
+    # of 60s to mitigate this problem.
+    #
+    # Since the TCP connection between the load balancer and this server doesn't
+    # totally reflect what the TCP connection between the client and load
+    # balancer is doing, measuring idle on this server is not very useful.
+    # Instead, network idle should be measured (and enforced) on the load
+    # balancer.
+    #
+    # If this value is too small, logs will appear in the error log:
+    #
+    #   The timeout specified has expired: ... mod_wsgi ... Failed to proxy response to client
+    Timeout 120
+
     RewriteEngine on
     RewriteRule ^/(.*)index.cgi/?(.*) https://hg.mozilla.org/$1$2
 
     SetEnv HGENCODING UTF-8
     SetEnv LC_TYPE UTF-8
 
     WSGIDaemonProcess hg.mozilla.org processes={{ wsgi_processes }} threads=1 maximum-requests=20 deadlock-timeout=60 inactivity-timeout=300 user=hg group=hg display-name=hg.mozilla.org
     WSGIProcessGroup hg.mozilla.org