CODEWITHSUNDEEP
apacheload-balancinghttpd.confmod-proxymod-proxy-balancer
USP-dos
USP-dos

Reputation: 93

Apache Load Balancer settings & graceful restarts

I've investigated the behavior of mod_proxy_balancer and graceful restarts. I've found out, that nearly every setting regarding load-balancing requires either A) a restart instead of a graceful restart, or B) give the balancer a new id, and then do a graceful restart to take effect.

I'll provide an example. Assume we have a loadbalancer configured like this:

<VirtualHost 22.11.22.11:443>
   ServerName       Hostname
   ProxyHCExpr isok {hc('body') =~ /==welcome ok1==/}
   ProxyHCTemplate template1 hcinterval=1 hcexpr=isok hcmethod=get hcuri=/healthcheck.php
   ProxyHCTemplate template2 hcinterval=1 hcexpr=isok hcmethod=head hcuri=/head_check.php
   <Proxy balancer:mybalancer>
     BalancerMember https://www.backend1.com:443 hctemplate=template1
     BalancerMember https://www.backend1.com:443 hctemplate=template1
   </Proxy>
<VirtualHost>

If we want to change the healthcheck template to "template2", this configuration does not work:

  <VirtualHost 22.11.22.11:443>
       ServerName       Hostname
       ProxyHCExpr isok {hc('body') =~ /==welcome ok1==/}
       ProxyHCTemplate template1 hcinterval=1 hcexpr=isok hcmethod=get hcuri=/healthcheck.php
       ProxyHCTemplate template2 hcinterval=1 hcexpr=isok hcmethod=head hcuri=/head_check.php
       <Proxy balancer:mybalancer>
         BalancerMember https://www.backend1.com:443 hctemplate=template2
         BalancerMember https://www.backend1.com:443 hctemplate=template2
       </Proxy>
    <VirtualHost>

but instead, if i do exactly the same AND rename the balancer, it will work after a graceful restart:

  <VirtualHost 22.11.22.11:443>
       ServerName       Hostname
       ProxyHCExpr isok {hc('body') =~ /==welcome ok1==/}
       ProxyHCTemplate template1 hcinterval=1 hcexpr=isok hcmethod=get hcuri=/healthcheck.php
       ProxyHCTemplate template2 hcinterval=1 hcexpr=isok hcmethod=head hcuri=/head_check.php
       <Proxy balancer:myNEWbalancer>
         BalancerMember https://www.backend1.com:443 hctemplate=template2
         BalancerMember https://www.backend1.com:443 hctemplate=template2
       </Proxy>
    <VirtualHost>

As i said this is for almost every loadbalancer related setting the same:

Tested with Apache v. 2.4.33.

Our strategy is now, to include all this settings into a hash, and then use the hash as balancer-id. Like this, whenever one of this settings is changed, the balancer gets a new id and the changes work. Is this a good solution? Has someone found a better workarround/solution for this, or some more insights why the balancer must be renamed? Restarting is no option for us..

i found bug reports that seem to be related to this:

https://bz.apache.org/bugzilla/show_bug.cgi?id=58529

https://bz.apache.org/bugzilla/show_bug.cgi?id=49771

and:

https://bz.apache.org/bugzilla/show_bug.cgi?id=55152

in the last one, it's stated that it is fixed, but still this problem appears in 2.4.33

Upvotes: 0

Views: 1224

Answers (1)

USP-dos
USP-dos

Reputation: 93

after an update of httpd to version 2.4.34 (released on monday, july 16, 2018) the issue does no longer appear! all the settings mentioned above can be changed and are successfully applied after a graceful restart.

Upvotes: 1

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