November 06, 2007

Web 2.0 operations

Artur Bergman – wikia

  • Operations builds trust in a brand.
  • Ops is the stepchild of engineering – development gets the glory.
  • To do good ops, you need sysadmins manning NOCs etc, and engineers.
  • Good engineers * Detail oriented * Don’t aspire to work in development * Should work with development though, so that both sides can learn about each other
  • You must understand the product to run it successfully. Complexity kills
  • http://www.debuggingrules.com/Debugging_CH2.PDF
  • Rule 3: Look first. You must have good monitoring and good alerting.
  • Do not over-alert, and do not cry wolf.
  • Trending – long term capactity planning. Make alerts be timely – there’s no point alerting at 90% on a 10TB partion that grows at 1MB a day
  • Websitepulse – gomez alternative.
  • Nagios – doesn’t scale well for large installations; doesn’t keep state; over-alerts
  • Hyperic – looks much nicer
  • Cricket / MRTG / Cacti – impossible to configure
  • Ganglia – rocks – no configuration
  • load increase while running process stays the same – shows up blocking calls
  • custom gmetric scripts – can collect more or less anything
  • graphing stuff is a very good way of spotting problems.
  • tcpdump / wireshark – tells you where packets are going wrong.
  • rule 4: Divide and conquer. Look at the problems in turn, go in the order you suspect is most likely
  • change one thing at a time, and keep an audit trail. use version control
  • If you didn’t fix it, it aint fixed. If it goes away, it will come back and bite you later. Figure out what happened.
  • use strace/dtrace/truss/gdb
  • you need a little bit of process.
  • Design against complexity. Re-use components, define standards. Have a few machine images, re-image all machines periodically for the hell of it
  • MTBF is irrelevant. dealing with failure is more important. Target the right level of uptime.
  • Don’t kid youself. You don’t need 5 nines
  • The higher you aim for reliability, the higher complexity and cost you’ll get. If you need 2 nines and aim for 5, you’ll do worse than if you just aim for 2
  • MTTR – a much better metric. 1 minute downtime every week is still 4 nines
  • Problem management: Once a problem is found, start a phone conference. Use IRC or IM to communicate technical info. Have one person liase with non-technical people, and one person be in command.
  • Write down results of root cause analysis
  • Automation: All machines are created equal. If you manually make changes, you are wrong (usually)
  • Best practice: * Gold images * Centralised authentication * NTP time sync * Central logging * All applies for virtual machines too!
  • cfengine – http://www.cfengine.org/ ; puppet is much nicer
  • cobbler – linux version of jumpstart
  • datacentres: keep them tidy; label everything. have a switch in each rack if you can. Remote consoles / Remote power switches save a lot of pain.
  • Virtualisation: Use it. Managing becomes much easier. power consumption goes down, new test boxes can be quickly provisioned
  • Loadbalancers: Keep them simple and low level. LVS + Squid Carp. http://docs.huihoo.com/gnu_linux/squid/html/x2398.html Log over UDP so you don’t block if the disk is full
  • Squid: Use for static stuff; use squid with a very short ttl (1 second) for non-logged-in-users and dynamic pages.
  • Databases: report slow queries. fear ORMs; understand what they are doing
  • If you’re small, outsource
  • http://www.pantherexpress.net/ : CDN
  • S3 for binlogs, datafiles, etc

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