[笔记]HAproxy reload config file with uninterrupt session

deer2010

　　HAProxy is a high performance load balancer. It is very light-weight, and free, making it a great option if you are in the market for a load balancer and need to keep your costs down.

　　Lately we’ve been making a lot of load balancer changes at work to accommodate new systems and services. Even though we have two load balancers running with keepalived taking care of any failover situations, I was thinking about how we go about>　　You are temporarily shutting your load balancer down
　　You are severing any current connections going through the load balancer
　　You might say, “if you have two load balancers with keepalived, restarting the service should be fine since keepalived will handle the failover.” This, however, isn’t always true. Keepalived uses advertisements to determine when to fail over. The default advertisement interval is 1 second (configurable in keepalived.conf). The skew time helps to keep everyone from trying to transition at once. It is a number between 0 and 1, based on the formula (256 – priority) / 256. As defined in the RFC, the backup must receive an advertisement from the master every (3 * advert_int) + skew_time seconds. If it doesn’t hear anything from the master, it takes over.
　　Let’s assume you are using the default interval of 1 second. On my test machine, this is the duration of time it takes to restart haproxy:
　　

time /etc/init.d/haproxy restart　　
Restarting haproxy haproxy
　　...done.
　　

　　
real    0m0.022s
　　
user    0m0.000s
　　
sys     0m0.016s
　　


　　In this situation, haproxy would restart much faster than your 1 second interval. You could get lucky and happen to restart it just before the check, but luck is not consistent enough to be useful. Also, in very high-traffic situations, you’ll be causing a lot of connection issues. So we cannot>　　After sifting through haproxy documentation (the text-based documentation, not the man page) (/usr/share/doc/haproxy/haproxy-en.txt.gz on Ubuntu), I came across this:
　　

    313　　314     global
　　315         daemon
　　316         quiet
　　317         nbproc  2
　　318         pidfile /var/run/haproxy-private.pid
　　319
　　320     # to stop only those processes among others :

　　321     # kill $(　　324     # breaking existing sessions :

　　325     # haproxy -f haproxy.cfg -p $(　　617
　　618  # haproxy -p /var/run/haproxy.pid -sf $(cat /var/run/haproxy.pid)
　　


　　The end-result is a>　　

# time haproxy -f /etc/haproxy.cfg -p /var/run/haproxy.pid -sf $(cat /var/run/haproxy.pid)　　

　　
real    0m0.018s
　　
user    0m0.000s
　　
sys     0m0.004s
　　


　　I’ve specified the config file I want to use and the pid file haproxy is currently using. The $(cat /var/run/haproxy.pid) takes the output of cat /var/run/haproxy.pid and passes it in to the -sf parameter as a list, which is what it is expecting. You will notice that the time is actually faster too (.012s sys, and .004s real). It may not seem like much, but if you are dealing with very high volumes of traffic, this can be pretty important. Luckily for us it doesn’t matter because we’ve been able to>
　　UPDATE: There is a>