{"id":5,"date":"2008-09-30T14:29:45","date_gmt":"2008-09-30T14:29:45","guid":{"rendered":"http:\/\/psyphi.net\/blog\/?p=5"},"modified":"2010-01-24T17:18:52","modified_gmt":"2010-01-24T17:18:52","slug":"apache-forward-proxy-remote_addr","status":"publish","type":"post","link":"https:\/\/psyphi.net\/blog\/2008\/09\/apache-forward-proxy-remote_addr\/","title":{"rendered":"Apache Forward-Proxy REMOTE_ADDR propagation"},"content":{"rendered":"

I had an interesting problem this morning with the Apache<\/a> forward-proxy supporting the WTSI<\/a> sequencing farm.<\/p>\n

It would be useful for the intranet service for tracking runs to know which (GA2) sequencer is requesting pages but because they’re on a dedicated subnet they have to use a forward-proxy for fetching pages (and then only from intranet services).<\/p>\n

Now I’m very familiar using the X-Forwarded-For header and HTTP_X_FORWARDED_FOR environment variable (and their friends) which do something very similar for reverse-proxies but forward-proxies usually want to disguise the fact there’s an arbitrary number of clients behind them, usually with irrelevant RFC1918 private IP addresses too.<\/p>\n

So what I want to do is slightly unusual – take the remote_addr of the client and stuff it into a different header. I could use X-Forwarded-For but it doesn’t feel right. Proxy-Via is also not right here as that’s really for the proxy servers themselves. So, I figured mod_headers on the proxy would allow me to add additional headers to the request, even though it’s forwarded on. Also following a tip I saw here<\/a> using my favourite mod_rewrite and after a bit of fiddling I can up with this:<\/p>\n

\r\n#########\r\n# copy remote addr to an internal variable\r\n#\r\nRewriteEngine  On\r\nRewriteCond  %{REMOTE_ADDR}  (.*)\r\nRewriteRule   .*  -  [E=SEQ_ADDR:%1]\r\n\r\n#########\r\n# set X-Sequencer header from the internal variable\r\n#\r\nRequestHeader  set  X-Sequencer  %{SEQ_ADDR}<\/code>\r\n<\/pre>\n
These rules sit in the container managing my proxy, after ProxyRequests and ProxyVia and before a small set of ProxyMatch restrictions.<\/p>\n
The RewriteCond traps the contents of the REMOTE_ADDR environment variable (it’s not an HTTP header – it comes from the end of the network socket as determined by the server). The RewriteRule unconditionally copies the last RewriteCond match %1 into a new environment variable SEQ_ADDR. After this mod_headers sets the X-Sequencer request header (for the proxied request) to the value of the SEQ_ADDR environment variable.<\/p>\n
This works very nicely though I’d have hoped a more elegant solution would be this:<\/p>\n
\r\nRequestHeader set X-Sequencer %{REMOTE_ADDR}<\/code>\r\n<\/pre>\n
but this doesn’t seem to work and I’m not sure why. Anyway, by comparing $ENV{HTTP_X_SEQUENCER} to a shared lookup table, the sequencing apps running on the intranet can now track which sequencer is making requests. Yay!<\/p>\n","protected":false},"excerpt":{"rendered":"
I had an interesting problem this morning with the Apache forward-proxy supporting the WTSI sequencing farm. It would be useful for the intranet service for tracking runs to know which (GA2) sequencer is requesting pages but because they’re on a dedicated subnet they have to use a forward-proxy for fetching pages (and then only from … Continue reading “Apache Forward-Proxy REMOTE_ADDR propagation”<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[17],"tags":[6,7,8,1080],"class_list":["post-5","post","type-post","status-publish","format-standard","hentry","category-sysadmin","tag-apache","tag-mod_rewrite","tag-proxy","tag-webdev"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t