Ellipsis

I’ve been following the "DevOps movement", since I was first turned on to Paul Hammond and John Allspaw’s "Velocity 2009 talk: 10+ Deploys Per Day: Dev and Ops Cooperation at Flickr":velocityconference.blip.tv/file/2284377/. Many of the precepts of their talk: infrastructure automation, automated deploys, version control, and shared metrics, have been part of my approach to system administration for some years now (albeit never to the extent that Flickr embraces these matters). So much of what they say, and what I see elsewhere in DevOps from following Chef and Puppet, resonates with an approach that I’m naturally tuned to. Not so much my workplace, despite nearly two years of quiet advocacy. Now, however, my workplace has come through the latest major release with more interest in evaluating how we do things than was the case during this last year’s headlong rush to a new architecture and infrastructure. So I scheduled a lunchtime session to view and discuss Hammond and Allspaw’s talk, and was pleased to have over two dozen people show up, and another handful call in to the conference line. Further, our senior VP watched the talk while he was on travel and responded that we should take seriously the direction in which Allspaw and Hammond point. I have no doubt the cultural hurdles will be harder to vault than the technological ones. But I have loved my work the best when I’ve been at the table with the developers from inception to deployment, and seen how well that works, so I’ll take heart from the positive response to this first small step. I’ll keep you posted.

At work we’re migrating several thousand research articles from Zope to another CMS. The CMS folks are taking care of moving the content, but when we’re done we’re going to institute a boatload of R=301 redirects from the old URLs to the new URLs.

RewriteMap is the accepted way with mod_rewrite of handling a lot of one-to-one mappings that don’t follow any particular pattern. What I figured out today was that I can use a rewrite map in a RewriteCond statement so I only do the redirect when there’s a match in the rewrite map lookup.

Here are some snippets from my httpd.conf to illustrate:

For testing, we’ll want logging:

RewriteLog /var/log/httpd/rewrite.log
RewriteLogLevel 2

Define the map we’re using. The content of the map is ‘old_uri new_uri’ with a space separating the two. Use .txt for testing, and the below we’ll convert to a DBM.

RewriteMap research_map txt:/etc/httpd/conf/research_map.txt 

Here, I got a hint from http://www.tunnell.org/blog_posts_view.php?blog_postid=3. Remember that the syntax for a RewriteCond is:

RewriteCond TestString ConditionPattern

TestString will be a map lookup of $1, where $1 is the match string of the following RewriteRule, expressed: ${research_map:$1}

For ConditionPattern, we will test if the TestString is lexically greater than ””, the empty string, which is what the map lookup returns when there’s no match. Expressed: >""

RewriteCond ${research_map:$1}  >""     # IE, if map result is greater than "" 

So if the URL starts with /research, then use the research_map value for the key $1 to redirect to new address

RewriteRule ^(/research/.*$) ${research_map:$1}      [R=301,L]

What we end up with is a few lines of configuration that quickly let me put in place 3342 new redirects. Here’s the whole stanza:

RewriteMap research_map txt:/etc/httpd/conf/research_map.txt 
RewriteCond ${research_map:$1}  >""     # IE, if map result is greater than "" 
RewriteRule ^(/research/.*$) ${research_map:$1}      [R=301,L]

# Same thing, but lookup with a trailing slash if there isn't one
RewriteCond ${research_map:$1/}  >"" 
RewriteRule ^(/research/.*[^/]$) ${research_map:$1/}      [R=301,L]

Lastly, converting the textfile to a dbm speeds up the lookup by at least an order of magnitude.