ATS (Apache Traffic Server) does not cache

Question

I am trying to make ATS cache return of my UWSGI Application which currently runs on the same machine as ATS itself.

I don't understand why ATS always forwards my requests to UWSGI and does not cache the results. I use ATS 5.1.1 on ubuntu 14.04 compiled from source and I followed a tutorial described here: http://daemonkeeper.net/735/apache-trafficserver-the-better-web-cache/

Using curl to make a test request, I always receive these diagnostics in the Via header: uScMsSf pSeN:t cCMi p sS

WHich can be decoded with traffic_via to:

Proxy request results:
Request headers received from client:               simple request (not conditional)
Result of Traffic Server cache lookup for URL:      miss (a cache "MISS")
Response information received from origin server:   served
Result of document write-to-cache:                  no cache write performed
Proxy operation result:                             served
Error codes (if any):                               no error
Operational results:
Tunnel info:                                        no tunneling
Cache-type and cache-lookup cache result values:    cache / cache miss (url not in cache)
ICP status:                                         no icp
Parent proxy connection status:                     no parent proxy
Origin server connection status:                    connection opened successfully

Can someone help me understand, why the result is not being cached?

My remap.config:

map http://trafficserver_build:8080 http://127.0.0.1:8888

My cache.config:

url_regex=.* revalidate=10m

My storage.config (default provided):

var/trafficserver 256M

Log requests state:

/opt/ts/bin/traffic_logcat -f /opt/ts/var/log/trafficserver/squid.blog


1415307115.252 0 10.0.3.28 TCP_MISS/200 258 HEAD http://127.0.0.1:8888/ - DIRECT/127.0.0.1 text/html
1415307127.721 0 10.0.3.28 TCP_MISS/200 258 HEAD http://127.0.0.1:8888/ - DIRECT/127.0.0.1 text/html
1415307171.141 0 10.0.3.28 TCP_MISS/200 258 HEAD http://127.0.0.1:8888/ - DIRECT/127.0.0.1 text/html
1415307176.480 0 10.0.3.28 TCP_MISS/200 258 HEAD http://127.0.0.1:8888/ - DIRECT/127.0.0.1 text/html

Answer 1

The most likely problem is that your origin is not setting the expected HTTP headers to make the response cacheable. The relevant Traffic Server setting is proxy.config.http.cache.required_headers, and the default is quite strict in requiring an Expires or Cache-Control header in the response.

https://trafficserver.readthedocs.org/en/latest/reference/configuration/records.config.en.html#proxy-config-http-cache-required-headers

Answer 2

You can also force content into cache by:

• setting proxy.config.http.cache.required_headers to 0; and
• configuring cache.config as per http://trafficserver.readthedocs.org/en/latest/reference/configuration/cache.config.en.html

So for example you could set cache.config to contain

dest_domain=mysite.com ttl-in-cache=10m

Combined with required_headers of 0, this will work even when you don't control the origin

Answer 3

Found it out... As James Peach points out I had to allow all requests to be cachable, but in addition the response must send the Vary header.