Initial implementation of health servlet
The health servlet allows the plugin to be used to return responses
to HAProxy's health check function [1]. For example if the http(s)
backend is configured with something like:
option httpchk GET /plugins/high-availability/health
then GET calls to the /health URL will return HTTP status 204, thus
indicating that the server is healthy (the default response).
Sending a DELETE request to the same /health URL will set the status
to 'unhealthy', and then any subsequent GET requests will return HTTP
503.
Sending a POST request sets the status back to 'healthy'.
Documentation and tests will be added in follow up changes.
[1] http://cbonte.github.io/haproxy-dconv/1.7/configuration.html#option%20httpchk
Change-Id: Ife2e6176347c5a84f328b9652a2613080572c994
3 files changed
