Scalability Articles

I read recently an excellent article where Randy Shoup of Ebay shares his "Scalability Best Practices".

Looks like some of the big websites have evolved in a similar way. Grown from simple, vertical, three tier-architectures (web-, app- and persistence-layer) to horizontal, service-oriented architectures with partitioned data layers (shards).

• Amazon 1 (podcast interview), 2, 3
• Google
  
• YouTube
• Flickr
• Digg

Enabling Compression in Tomcat

With apache I was used to mod_deflate. After switching to just tomcat I started to look for a gzip servlet filter when I noticed that you can configure gzip in your server.xml per Connector. This means you can have different gzip configurations for port 80 and ssl port 443.

Example configuration:

<connector port="80" protocol="HTTP/1.1" enablelookups="false" connectiontimeout="60000" maxthreads="150" compression="on" compressionminsize="2048" compressablemimetype="text/html,text/xml,text/javascript,application/x-javascript,application/javascript,text/css" redirectport="443">

This enables compression for all requests on port 80 where the response is of a certain mime type and is larger than 2k.

Link to the tomcat documentation regarding this.

Moving SSL certificate from Apache to Tomcat

I finally managed to move our ssl certificates, from apache to tomcat.

First I just tried to import the existing openssl cert using the keytool. I failed miserably, gave up and went down the reissue road.

Which turned out to be really simple, even though it took thawte 2 days and a live chat before I received the new cert. And then, the live openssl certificate stopped to work! So all of a sudden I hade to switch to the pure tomcat solution a bit head of schedule.. Luckily I've had that working for while now with functional and load tests already made.

1. Create your java keystore with a tomcat keyentry.
   keytool -genkey -keyalg RSA -alias tomcat -keystore [keystore name]



2. Generate a CSR and submit it to Thawte, using the reissue form.
   keytool -certreq -alias tomcat -keyalg RSA -file certreq.csr -keystore [keystorename]



3. Wait a couple of days, receive the new cert and save it into a file on your server



4. Import the cert into your tomcat keystore
   keytool -import -alias tomcat -trustcacerts -file mythawtecert.txt -keystore [keystorename]



5. Configure server.xml
   <connector port="443" protocol="HTTP/1.1" sslenabled="true"
maxthreads="150" scheme="https" secure="true"
clientAuth="false" sslProtocol="TLS" keystoreFile="conf/tomcat.keystore" keystorePass="xxxx">

Basically, to reissue is almost like creating new certificate, except for having to pay for it. For more details, check out Thawte's supportpage.

Switching to a pure tomcat setup

Today I transfered our website to some new servers. I decided run a pure tomcat setup without apache in front. The problem is that the apache server did some critical and some less critical stuff that I haven't tried doing with just tomcat before (I've written the corresponding apache module in parenthesis):

• SSL (mod_ssl)
  
• Url redirection, critical for url canonization (mod_rewrite)
  
• Gzip compression (mod_deflate)
• Setting the correct cache-headers (mod_expires, mod_headers)