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Hi,
even if this now is becoming a boring question, and even if
its already handled by the documentation I would like to
suggest the following method for monitoring:
Just to explain what I am doing in ldirectord for http:
Every second on the real server I try to open a socket on port
80 and immediatly close it. If that fails, ldirectord takes
the real server out.
Every 30 seconds ldirectord does a real HTTP-request and checks
if the result is correct. The first method does not pollute
the web-server logfiles, the second can be used to check integrety, but
is much slower and creates much more overhead. Therefore
I do it only all 30 seconds.
I agree that there is nothing the kernel can do, such as the second check.
But the first one (socket-alive) can be avoided. I try to explain how:
typical TCP/IP connection
Time Client Server Comment
| | |
v |----- SYN isn1 --------->| initiate connection
|<- SYN isn2 ACK isn1+1 --| this my not pass through the
LB
| |
** CHECK HERE: |----- ACK isn2+1 ------->|
| |
|<----- ACK, DATA ------->|
|<----- ACK, DATA ------->|
.........
|<----- ACK, DATA ------->|
| |
|------ FIN isn3 -------->|
|<---- ACK isn3+1 ------->|
|<---- FIN isn4 --------->|
|------ ACK isn4 -------->|
What the LB could do is to check the timediff between "SYN isn1" and "SYN
isn2 ACK isn1+1".
But this packet may not return through the LB, when configured as tunnel or
gate.
But LVS could check for "ACK isn2+1". If that time expires, You can bet that
the real server
is dead. Then You may set its weight to lets say -weight and give the
responsability to
the monitoring software, which may readd the realserver after is came back.
I think it should not be too difficult to implement this, or am I wrong?
Jacob
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