Backend health polling with client or round-robin

[Hugo Cisneiros (Eitch)]

On Tue, Apr 3, 2012 at 3:59 PM, Justin Davis
<justindavis at mail.utexas.edu> wrote:
> Is "/server-status?auto" an appropriate URL to use for backend health polling with a client or round-robin director?
>
> We recently had one of our two load balanced servers go belly-up, during which Varnish continued attempting to server content from the failed node.
>
> Would a small file be preferable? It's my understanding that a backend node is marked as unhealthy if the health check times out or returns a status other than 200 more than the configured threshhold times per configured window.

>From what I understand, it depends on what is running on your web
server. For example, if it's only static files, a small file that
returns HTTP 200 is ok. If it's a dynamic system, the recommended way
is a page that checks if the components of the system are ok (like 'is
it using the database sucessfully?'; 'are the permissions on the
server-managed folder ok?', and so on).

Sometimes a system can go all wrong, but a static page will still
return HTTP 200 for varnish, thus varnish will still be delivering
requests to the server/system.

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