not support dynamic add/delete detect node and found some bugs

[alexzzh]

Our project needs to use the proactive health detect function and may need to be combined with the thid-part dynamic domain name resolution module to dynamically adding or deleting upstream nodes. but ngx_healthcheck_module does not support dynamic APIs and has some bugs. so develop a new module .

• ngx_healthcheck_module bugs after test in our project, Just for your reference
  • When the connection fails, the connection state and the shared memory node state are not cleaned up and ngx_stream_upstream_check_clean_event need to be called
  • At this point, the shared memory array index should be displayed instead of the process-local array Index, which will cause the status index returned by each process to be inconsistent，i ==> peer[i].index
  • It grows itself every time, causing shared memory data to never be reused
  • If the detection mode is TCP, you cannot configure long and short connections
  • When querying the status, the parameter index is the index of the shared memory array, which should not be compared with the number of local arrays of the process, the number of shared memory arrays should be compared, and there is no judgment on whether peer[index].delete is 1 to filter deleted nodes
  • The peer[index].delete flag is not first judged to filter deleted nodes
  • Data is not protected by lock when accessing shared memory 1
  • Data is not protected by lock when accessing shared memory 2