Apache Performance Tuning: Scaling Out
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This document discusses Apache performance tuning, focusing on scaling out through redundancy, load balancing, and caching strategies. Key techniques include vertical and horizontal scaling, various load balancing schemes like DNS round-robin and peer-based methods, as well as session state management to address issues arising from stateless HTTP. The document emphasizes the importance of monitoring for outages and performance to ensure reliability and scalability in server configurations.
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Apache Performance Tuning: Scaling Out
- 1. Apache Performance Tuning Part 2: Scaling Out Sander Temme <[email protected]>
- 2. Agenda • Introduction • Redundancy in Hardware • Building Out: Separate Tiers • Building Out: Load Balancing • Caching Content • Conclusion
- 3. Introduction • Why do This? – Scalability (Oh my gosh, I’m so popular!) – Reliability (We need five nines!) • Why NOT do This? – It costs money
- 4. Redundancy in Hardware • Moving Parts Break – Hard Disks – Power Supplies – Hard Disks – Fans – Hard Disks • Buy High Quality Disks – Refurbished, OEM, Brand Name – Which has longer warranty? – Which is more reliable?
- 5. Server Configuration • Mirror those Disks – Install the RAID utility – Have it warn you – RAID is no good if you don’t learn of failures! • Redundant Power Supplies – On different circuits
- 7. Scaling Vertically • Move Services to Other Hosts • Pros: – Less resource contention – Specialized hardware – Scale out tiers individually • Cons: – Development/Deployment harder – More hosts to manage
- 9. Scaling Horizontally • Multiple servers per tier • All receive requests • All serve same content • Some arbitration scheme
- 10. Load Balancing Schemes • DNS Tricks • Peer Server Pools – Network Load Balancing (Win2k3) – Wackamole • Load Balancing Appliance – Box from F5, Juniper, Cisco, Foundry, … – Linux Virtual Server
- 11. DNS Round-Robin • Easy! • Multiple A Records in DNS Zone File • Not Smart: – DNS Lookups are cached – Load on Server – Server Outage
- 12. Example Zone File scalingout.org. 86400 IN SOA ns.scalingout.org. sctemme.scalingout.org. ( 2006051401 ; Serial 86400 ; refresh (1 day) 7200 ; retry (2 hours) 8640000 ; expire (10 days) 86400 ) ; minimum (1 day) scalingout.org. IN NS bagheera.scalingout.org. gw IN A 10.11.0.1 bagheera IN A 10.11.0.2 ; ... mail IN CNAME bagheera ns IN CNAME bagheera www IN A 10.11.0.113 IN A 10.11.0.114 IN A 10.11.0.115
- 13. Peer-based: NLB • Windows 2000 Server Enterprise Ed., Windows Server 2003 • Up to 32 hosts in cluster • All hosts assume cluster IP, MAC • NLB makes LB decision – Only one host gets to answer TCP handshake • Should be application independent
- 14. Peer-based: Wackamole • High Availability Solution • When Host Fails – Other hosts take over its IP addresses – Distribute IP addresses among cluster – Every IP address reliably available • No Load Balancing! – Use with RR DNS (or something) http://www.backhand.org/wackamole/
- 15. Load Balancing Device Client Internet
- 16. Load Balancing • One Load Balancer • Many Web Servers • Choice of Balancing Schemes – Round-robin, Least Used, … • Reliability – Heartbeats, unavailable servers don’t receive requests • Feature War
- 17. Linux Virtual Server • Free, Open Source, etc. • IP Virtual Server module in kernel • Lots of auxiliary modules – Like a box of Legos – May come with Your Distribution • Do It Yourself http://www.linuxvirtualserver.org/
- 18. Example: mod_proxy_balancer • New in Apache HTTP Server 2.2 • Part of mod_proxy • Two Load Balancing Methods – By number of requests – By number of bytes • Detects failed backends
- 19. Apache Configuration Listen 80 LogLevel debug TransferLog logs/access_log LoadModule proxy_module modules/mod_proxy.so LoadModule proxy_http_module modules/mod_proxy_http.so LoadModule proxy_balancer_module modules/mod_proxy_balancer.so ProxyPass / balancer://mycluster/ ProxyPassReverse / http://1.2.3.4:80 ProxyPassReverse / http://1.2.3.5:80 <Proxy balancer://mycluster> BalancerMember http://1.2.3.4:80 BalancerMember http://1.2.3.5:80 </Proxy>
- 20. Example: Tomcat, mod_jk • Apache + mod_jk • Multiple Tomcat servers • Balancer Worker
- 21. Apache Configuration LoadModule jk_module /Volumes/Files/asf/httpd-r415210w/modules/mod_jk.so JKMount /servlets-examples/* loadbalancer JKMount /*.jsp loadbalancer JkMount /jkmanager/* jkstatus JKLogFile logs/jk_log JKLogLevel debug JKWorkerProperty worker.list=loadbalancer,jkstatus JKWorkerProperty worker.tc1.port=15109 JKWorkerProperty worker.tc1.host=localhost JKWorkerProperty worker.tc1.type=ajp13 JKWorkerProperty worker.tc1.lbfactor=1 JKWorkerProperty worker.tc2.port=15209 JKWorkerProperty worker.tc2.host=localhost JKWorkerProperty worker.tc2.type=ajp13 JKWorkerProperty worker.tc2.lbfactor=1 JKWorkerProperty worker.tc3.port=15309 JKWorkerProperty worker.tc3.host=localhost JKWorkerProperty worker.tc3.type=ajp13 JKWorkerProperty worker.tc3.lbfactor=1 JKWorkerProperty worker.loadbalancer.type=lb JKWorkerProperty worker.loadbalancer.balance_workers=tc1, tc2, tc3 JKWorkerProperty worker.jkstatus.type=status
- 22. Tomcat Configuration • Put same content on all Tomcats • Edit conf/server.xml: <Engine name="Catalina" defaultHost="localhost" jvmRoute="tc1"> • jvmRoute must match jk worker name!
- 23. Problem: Session State • HTTP is Stateless • Apps use Sessions – Cookies – URL Encoding • Session created on single server – Broken by Load Balancing – PHP: sessions stored on disk
- 24. Solutions: Session State • “Sticky” routing on Load Balancer • Store State in DB • Put benign State in Cookie – But don’t trust the client too much • Replicate Sessions on Back-end
- 25. Tomcat Session Replication • Share HttpSession objects across instances • One instance dies, session lives on • Apache will route requests to other instance • Uses IP Multicast
- 26. Session Replication Config • Uncomment <Cluster> element in server.xml • Put empty <distributable /> element in <web-app> element in web.xml
- 27. Caching Content • Dynamic Content is Expensive • Static Content Relatively Cheap • Several Approaches: – Dynamic caching – Pre-rendering popular pages (index.rss…) 27
- 28. mod_cache Configuration <IfModule mod_cache.c> <IfModule mod_disk_cache.c> CacheRoot /raid1/cacheroot CacheEnable disk / # A page modified 100 min. ago will expire in 10 min. CacheLastModifiedFactor .1 # Always check again after 6 hours CacheMaxExpire 21600 </IfModule> </IfModule> 28
- 29. Make Popular Pages Static • RSS Feeds • Popular catalog queries • … (Check your access log) 29
- 30. Static Page Substitution <Directory "/home/sctemme/inst/blog/httpd/htdocs"> Options +Indexes Order allow,deny Allow from all RewriteEngine on RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule ^(.*)$ /cgi-bin/blosxom.cgi/$1 [L,QSA] </Directory> 30
- 31. Tuning the Database Tier • Not my area (sorry) • Give Money to Oracle Consultants – (or MySQL) (or …) • Tip: Separate Read and Write Operations – Replicate from Write db to Read db – Read db data slightly stale • Does it matter?
- 32. Putting it All Together Read-only Internet Client Write-only
- 33. Monitoring the Farm • Monitor for outages – More boxes, more failure – HA can mask failures • Monitor for performance – Utilization – Trends
- 34. Monitoring Solutions • Nagios – Check services, hosts for outage – Highly configurable, extendable – Worth your time investment • Ganglia – Monitor for performance – See Brad Nicholes’s session
- 35. Monitoring Caveats • Takes Time, Effort – Highly flexible products • You can’t fix it – If you don’t know it’s broken • You can’t tune it – If you don’t know the bottlenecks
- 36. Conference Roadmap • Monitoring 2.0 - Zenoss, the next level of IT management (Training) • Apache Performance Tuning Part 1: Scaling Up • Load-balancing with Apache HTTPD 2.2 and later • Scaling the download infrastructure with your success • Break My Site
- 38. Thank You