So I've been wanting a failover solution for log receivers and currently
nxlog-ce doesn't have an answer, but I think I found a hack that might work:
the reroute() command. Here's what I did:
The first thing that we need to do is to create the alternate route. In order
to create the route statement without errors, I created a NULL input. Basically
this route doesn't do anything until called upon later.
<Input in_null>
Module im_null
</Input>
<Route route_alternate>
Path in_null => out_alternative
</Route>
The second thing we need to create is a buffer module. The buffer will sit
between the default input and the default output and act as the detection
method for problems. If the default output blocks (e.g. the tcp connection
dies), the buffer will start filling.
<Processor buffer>
Module pm_buffer
MaxSize 2048
Type Mem
Exec if buffer_count() > 2 reroute("route_alternative");
</Processor>
<Route route_default>
Path in_default => buffer => out_default
</Route>
The EXEC statement in this block says that if the number of log entries in the
buffer exceeds a certain amount (in my test case, 2 messages), reroute the
message to the alternative path.
With my limited testing, I see having 2 potential benefits with 1 potential
drawback. The first benefit is, of course, failover. If the default route dies,
the reroute statement will send the message elsewhere. The second benefit is
log spike protection. If a sudden spike in log messages happens and the default
route can't handle the load, the buffer will fill and the alternative route
will start processing messages. The only drawback I can see is that there will
be messages stuck in the buffer and when they finally clear the buffer, might
be late. This may cause problems with any real-time process you may be doing on
the backend (e.g. real-time alerts).
Thoughts?
Justin
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