Apache Traffic Server

Apache Traffic Server is a caching proxy server.

Basic configuration

The basic changes to the default configuration required to get a caching proxy are:

# /etc/trafficserver/remap.config
map http://127.0.0.1:3128/ http://$origin_server_ip/
reverse_map http://$origin_server_ip/ http://127.0.0.1:3128/

The following rule can be used as a catchall for mapping any request to a given origin server:

# /etc/trafficserver/remap.config
map / http://deployment-mediawiki05.deployment-prep.eqiad.wmflabs/

# /etc/trafficserver/records.config
CONFIG proxy.config.http.server_ports STRING 3128 3128:ipv6
CONFIG proxy.config.http.cache.required_headers INT 1
CONFIG proxy.config.url_remap.pristine_host_hdr INT 1

If proxy.config.http.cache.required is set to 2, which is the default, the origin server is required to set an explicit lifetime, from either Expires or Cache-Control: max-age. By setting required_headers to 1, objects with Last-Modified are considered for caching too. Setting the value to 0 means that no headers are required to make documents cachable.

Cheatsheet

Show non-default configuration values:

sudo traffic_ctl config diff

Configuration reload:

sudo traffic_ctl config reload

Lua scripting

ATS plugins can be written in Lua. As an example, this is how to choose an origin server dynamically:

# /etc/trafficserver/remap.config
map http://127.0.0.1:3128/ http://$origin_server_ip/ @plugin=/usr/lib/trafficserver/modules/tslua.so @pparam=/var/tmp/ats-set-backend.lua
reverse_map http://$origin_server_ip/ http://127.0.0.1:3128/

-- /var/tmp/ats-set-backend.lua
function do_remap()
    url = ts.client_request.get_url()
    if url:match("/api/rest_v1/") then
        ts.client_request.set_url_host('origin-server.eqiad.wmnet')
        ts.client_request.set_url_port(80)
        ts.client_request.set_url_scheme('http')
        return TS_LUA_REMAP_DID_REMAP
    end
end

External links

• https://docs.trafficserver.apache.org/en/latest/admin-guide/files/records.config.en.html
• https://docs.trafficserver.apache.org/en/latest/admin-guide/files/remap.config.en.html
• https://docs.trafficserver.apache.org/en/latest/admin-guide/plugins/ts_lua.en.html