Hi guys, I was researching/testing Knox HA with Apache HTTP Server + mod_proxy + mod_proxy_balancer. Here is what I found. I. 3 load balancer scheduler algorithms available for use: Request Counting, Weighted Traffic Counting and Pending Request Counting. ( http://httpd.apache.org/docs/2.2/mod/mod_proxy_balancer.html#scheduler) II. Load balancer stickyness. ( http://httpd.apache.org/docs/2.2/mod/mod_proxy_balancer.html#stickyness) I configured and tested stickyness. Worked as it had to be. III. Failover. ( http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#proxypass) 1. I ran foolowing use cases: a) Knox instance is down before client request comes in. Steps: - Configure Apache HTTP Server to proxy two Knox instances; - Shoot down Knox instance A; - Execute client request; - Verify that Knox instance A is marked as unavailable and client's request is redirected to Knox instance B; - Verify that all subsequent requests in scope of the same client's session are passed just to Knox instance B; - Verify that client's requests in scope of new session are tried to be passed to Knox instance A. It is required because Knox instance A could be started before new client's session. This use case works fine. b) Knox instance goes down when it processes client's PUT request. Steps: - Start executing PUT file to HDFS with medium size (200Mb); - After some time shoot down Knox instance which processes this request; - Verify that client gets 500 status code and no failover takes place. This use case works as it is described. Apache HTTP Server is not able to do failover in this case. c) Knox instance goes down when it processes client's GET request. Steps: - Start executing GET file from HDFS with medium size (200Mb); - After some time shoot down Knox instance which processes this request; - Verify that client gets 200 status code, 'Content-Length' header with value equals to file size and some bytes in the body. To execute this test I used as a client: 1) HttpClient - it doesn't produce any error when stream is closed. 2) CURL - it doesn't produce any error when stream is closed. 3) Firefox browser - it doesn't produce any error when stream is closed. All clients just download available bytes before stream is closed, so client has to manually compare 'Content-Length' header value and received bytes length. - No failover takes place. This use case works as it is described. Apache HTTP Server is not able to do failover in this case. 2. Additional use cases. What new cases could you advise? IV. What functionality did I miss?
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