Hefta-Gaub Development Blog

April 10, 2008

More EC2 Tools/Notes

Filed under: Uncategorized — zappoman @ 8:15 pm

Couple of random notes…

1) AWS Tools – This is a great set of command line tools for accessing S3 and EC2. I’ve only played with the S3 features, but they are great and make it a lot easier to implement some of my backup and restore to s3 features I am building on my Ec2 cloud/array

2) Ec2 First Run – Ok, this is totally obvious when you think about it, but it took me a couple days of scratching my head wondering why this wasn’t working before I had the “duh” moment. Mind you, I didn’t work on trying to solve this problem for 2 days, because I was working on other things… but it wasn’t obvious to me for a couple of calendar days. What the heck am I talking about!?!?! This:

  • I wanted to build a custom AMI that would do a bunch of stuff on first run. Mostly create my lvm volumes, download a backup of my Database from S3, send me notification that it was up and running, stuff like that.
  • The rc.local of the existing AMI has this nice little section of code labeled “first run” and it purports to do stuff on first run only, while the rest of rc.local would run on a reboot of the instance as well. Simple right? So I code up my first run shell scripts and get them all happy, drop them in the if branch of the code… build my AMI… launch a new instance… and (silence) nothing happens…. huh? Why’s that. Let’s look at the code:
    # This script will be executed *after* all the other init scripts.
    # You can put your own initialization stuff in here if you don't
    # want to do the full Sys V style init stuff.
    # Stuff we want to do once at launch and never again:
    if [ -f "/root/firstrun" ]; then
        # do my stuff here --
        # create our logical volumes
        # restore from my latest backups
        # send our admin team a notification
        # do some more stuff here -- from the orginal AMI
        rm -f /root/firstrun
  • Well, it should have been obvious, but this code only runs if a file “/root/firstrun” exists, and at the end of the code, the code deletes that file. Well, since I made this AMI from a running instance, the first run had already run, and therefore “/root/firstrun” didn’t exist… DUH!
  • So, I touched /root/firstrun and rebuilt my AMI, and now first run actually works. I need to remember to do this before I rebuild my AMI again.

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