The IBM Knowledge Center has a nice chapter on "Informing users of a migration or update". You basically redirect everyone to a static maintenance page unless they arrive from a certain IP adress (so you as an administrator can still work):

LoadModule rewrite_module modules/mod_rewrite.so
RewriteEngine on

RewriteCond %{REMOTE_HOST} !^127.0.0.1

RewriteCond %{REMOTE_HOST} !^192.168.157.139

RewriteCond %{REMOTE_HOST} !^192.168.157.140

RewriteRule !^/upgrading.htm$ /upgrading.htm [L,R=500]

ErrorDocument 500 /upgrading.htm

Unfortunately, in a current customer project, that did not work for me, as this
  • blocked the healtcheck from the Load Balancer (LB) in front of Connections as well, which resulted in the requests not getting forwarded to the IHS
  • "%{REMOTE_HOST}" always being the IP of the load balancer

So I had to modify the statement a little bit:
LoadModule rewrite_module modules/mod_rewrite.so
RewriteEngine on

RewriteCond %{REMOTE_HOST} !^127.0.0.1

# Allow traffic from the Healthcheck host aka. Load Balancer ...

RewriteCond %{REMOTE_HOST} !^10.1.1.22

RewriteCond %{REMOTE_HOST} !^10.1.1.21

# Check the "X-Forwarded-For" http header for the original IP of the requester

# and block if not certain IP (add more lines for more IPs)

RewriteCond %{HTTP:X-Forwarded-For} !^192.168.157.139

RewriteCond %{HTTP:X-Forwarded-For} !^192.168.157.140
RewriteRule !^/upgrading.htm$ /upgrading.htm [L,R=500]

ErrorDocument 500 /upgrading.htm

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This is the Blog of Martin Leyrer, currently employed as IT-Specialist at IBM Austria - IBM Software Group, IBM Collaboration Solutions.

The postings on this site are my own and do not represent the positions, strategies or opinions of any former, current or future employer of mine.