Hi all,
We've been working on a new feature for Traffic Router that will add
support for providing multiple locations in the response to a client
for HTTP delivery services. Phil has proposed a spec for the response
format, which is roughly comprised of the following:
1) 302 redirect
2) Location header with the preferred endpoint URL
3) JSON response body containing multiple URLs, the first URL is the
same as the Location header
We've built this feature on top of the steering delivery feature, but
extended it to allow us to return a list of URLs based on the
subordinate delivery services instead of a single endpoint based on
one of the subordinate delivery services. We use the same code and
consistent hashing, but we now include, in order, the "best" endpoint
across all subordinate delivery services.
The following is an example request if we have a multi-location
steering delivery service, foo, and two subordinates: foo-a, foo-b,
noting the two different delivery services in the JSON body:
> GET /a HTTP/1.1
> Host: tr.foo.cdn.example.com
> User-Agent: curl/7.43.0
> Accept: */*
>
< HTTP/1.1 302 Moved Temporarily
< Server: Apache-Coyote/1.1
< Location: http://cache-01.foo-a.cdn.example.com/a
< Content-Type: application/json
< Content-Length: 149
< Date: Wed, 01 Mar 2017 18:00:11 GMT
<
{ [149 bytes data]
* Connection #0 to host localhost left intact
{
"locations" : [
"http://cache-01.foo-a.cdn.example.com/a;,
"http://cache-01.foo-b.cdn.example.com/a;
]
}
Another important implementation detail is that not all HTTP client
libraries are able to parse a JSON body when a 302 response and
Location header are present. Because of this, we are also allowing a
query parameter, currently "redirect=false", which will cause a 200
response with no Location header. This is similar to the "format=json"
query parameter precedent that we currently allow for
non-multi-location responses.
In Traffic Ops, we will introduce a new type called "CLIENT_STEERING"
and an additional boolean value in the steering.json API endpoint
called clientSteering. Traffic Router will consume this, see the value
and serve a multi-location response if set to true.
Phil's draft can be found here: https://github.com/PSUdaemon/multi-location
Questions/comments welcome.
--
Thanks,
Jeff
