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/

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

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