Designing, Scoping, and Configuring Scalable Drupal Infrastructure. Presented by David Strauss

Transcription

1 Designing, Scoping, and Configuring Scalable Drupal Infrastructure Presented by David Strauss

2 Understanding Load Distribution

3 Predicting peak traffic Traffic over the day can be highly irregular. To plan for peak loads, design as if all traffic were as heavy as the peak hour of load in a typical month -- and then plan for some growth.

4 Analyzing hit distribution 100% Dynamic Pages Static Content 30% Anonymous 50% Web Crawler Human 10% 40% No Special Treatment Pay Wall Bypass 3% 70% Authenticated 20% 7%

5 Throughput vs. Delivery Methods Green (Static) Yellow (Dynamic, Cacheable) Red (Dynamic) Content Delivery Network 2 Reverse Proxy Cache Drupal + Page Cache + memcached Drupal + Page Cache 1000 req/s 1 1 Drupal 1 10 req/s More dots = More throughput 1 2 Delivered by Apache without Drupal Some actually can do this.

6 Objective Deliver hits using the fastest, most scalable method available.

7 Layering: Less Traffic at Each Step Your Datacenter Traffic Load Balancer Reverse Proxy Cache DNS Round Robin CDN Database

8 Offload from the master database Search Your master database is the single greatest limitation on scalability. Slave Database Memory Cache Master Database

9 Tools to use Apache Solr for search. (Acquia offers hosting of this now.) Squid or Varnish for reverse proxy caching. Any third-party service for CDN.

10 Do the math All non-cdn traffic travels through your load balancers and reverse proxy caches. Even traffic passed through to application servers must run through the initial layers. Traffic Load Balancer Reverse Proxy Cache What hit rate is each layer ge ing? How many servers share the load?

11 Get a management/monitoring box Load Balancer (maybe two or three and have them specialized or redundant) Database Management Reverse Proxy Cache

12 Planning + Scoping

13 Infrastructure goals Redundancy Scalability Performance Manageability

14 Redundancy When one server fails, the website should be able to recover without taking too long. This requires N+1, putting a floor on system requirements. How long can your site be down? Automatic versus manual failover

15 Performance Find the sweet spot for hardware. This is the best price/performance point. Avoid overspending on any type of component Yet, avoid creating bottlenecks Swapping memory to disk is very dangerous

16 Relative importance Processors/Cores Memory Disk Speed Reverse Proxy Cache Web Database Monitoring

17 Reverse proxy caches Squid makes poor use of multiple cores. Focus on getting the highest per-core performance. The best per-core performance is often on dual-core processors with high clock rates and lots of cache. Varnish is much more multithreaded. 4-8 GB memory, total Expect 1000 requests per second, per Squid 64-bit operating system if more than 2 GB RAM

18 Web servers Apache mod_php + memcached Many processors + many cores is best 25 Apache threads per core 50 MB memory per thread, system-wide 1 GB memory for system 1 GB memory for memcached Configure MaxClients in Apache to maximum system-wide thread count Expect 1 request per thread, per second

19 Database servers MySQL 5.0 cannot use more than eight cores effectively but gets good gains from at least quadcore processors. Depend on each Apache thread needing one connection, and add another 50. Each MySQL connection needs around 6 MB. MySQL with InnoDB needs a buffer pool large enough to cache all indexes. Start by giving the pool most remaining database server memory and working from there. 64-bit operating system if more than 2 GB RAM

20 Monitoring server Very low hardware requirements Choose hardware that is inexpensive but essentially similar to the rest of the cluster to reduce management overhead Reliability and fast failover are typically low priorities for monitoring services

21 Assembling the numbers Start with an architecture providing redundancy. Two servers, each running the whole stack Increase the number of proxy caches based on anonymous and search engine traffic. Increase the number of web servers based on authenticated traffic. Databases are harder to predict, but large sites should run them on at least two separate boxes with replication.

22 Pressflow Make Drupal sites scale by upgrading core with a compatible, powerful replacement.

23 Common large-site issues Drupal core requires patching to effectively support the advanced scalability techniques discussed here. Patches often conflict and have to be reapplied with each Drupal upgrade. The original patches are often unmaintained. Sites stagnate, running old, insecure versions of Drupal core because updating is too difficult.

24 What is Pressflow? Pressflow is a derivative of Drupal core that integrates the most popular performance and scalability enhancements. Pressflow is completely compatible with existing Drupal 5 and 6 modules, both standard and custom. Pressflow installs as a drop-in replacement for standard Drupal. Pressflow is free as long as the matching version of Drupal is also supported by the community.

25 What are the enhancements? Reverse proxy support Database replication support Lower database and session management load More efficient queries Testing and optimization by Four Kitchens with standard high-performance software and hardware configuration Industry-leading scalability support by Four Kitchens and Tag1 Consulting

26 Four Kitchens + Tag1 Provide the development, support, scalability, and performance services behind Pressflow Comprise most members of the Drupal.org infrastructure team Have the most experience scaling Drupal sites of all sizes and all types

27 Ready to scale? Learn more about Pressflow: Pick up pamphlets in the lobby Request Pressflow releases at fourkitchens.com Get the help you need to make it happen: Talk to me (David) or Todd here at DrupalCamp

28 Managing the Cluster

29 The problem So ware and Configuration Objectives: Fast, atomic deployment and rollback Minimize single points of failure and contention Restart services Integrate with version control systems

30 Manual updates and deployment Human Human Human Human Human Why not: slow deployment, non-atomic/difficult rollbacks

31 Shared storage NFS Why not: single point of contention and failure

32 rsync Synchronized with rsync Why not: non-atomic, does not manage services

33 Capistrano Deployed with Capistrano Capistrano provides near-atomic deployment, service restarts, automated rollback, test automation, and version control integration (tagged releases).

34 Multistage deployment Deployed with Capistrano Deployments can be staged. cap staging deploy cap production deploy Deployed with Capistrano Development Integration Deployed with Capistrano Staging

35 But your application isn t the only thing to manage.

36 Beneath the application Reverse Proxy Cache Cluster-level configuration Database Cluster management applies to package management, updates, and so ware configuration. cfengine and bcfg2 are popular cluster-level system configuration tools.

37 System configuration management Deploys and updates packages, cluster-wide or selectively. Manages arbitrary text configuration files Analyzes inconsistent configurations (and converges them) Manages device classes (app. servers, database servers, etc.) Allows confident configuration testing on a staging server.

38 All on the management box Integration Staging Management{Development Deployment Tools Monitoring

39 Monitoring

40 Types of monitoring Failure Capacity/Load Analyzing Downtime Viewing Failover Troubleshooting Notification Analyzing Trends Predicting Load Checking Results of Configuration and So ware Changes

41 Everyone needs both.

42 What to use Failure/Uptime Capacity/Load Nagios Hyperic Cacti Munin

43 Nagios Highly recommended. Used by Four Kitchens and Tag1 Consulting for client work, Drupal.org, Wikipedia, etc. Easy to install on CentOS 5 using EPEL packages. Easy to install nrpe agents to monitor diverse services. Can notify administrators on failure. We use this on Drupal.org

44 Hyperic I haven t used this much, but it s fairly popular. More difficult to set up than Nagios.

45 Cacti Highly annoying to set up. One instance generally collects all statistics. (No agents on the systems being monitored.) Provides flexible graphs that can be customized on demand. Optimized database for perpetual statistics collection. We use this on Drupal.org and for client sites.

46 Munin Fairly easy to set up. One instance generally collects all statistics. (No agents on the systems being monitored.) Provides static graphs that cannot be customized.

47 Cluster Problems

48 Cache/session coherency Systems that run properly on single boxes may lose coherency when run on a networked cluster. Some caches, like APC s object cache, have no ability to handle network-level coherency. (APC s opcode cache is safe to use on clusters.) memcached, if misconfigured, can hash values inconsistently across the cluster, resulting in different servers using different memcached instances for the same keys. Session coherency can be helped with load balancer affinity.

49 Cache regeneration races Downside to network cache coherency: synched expiration Hard to solve All servers regenerating the item. { Old Cached Item New Cached Item Time Expiration

50 Broken replication MySQL slave servers get out of synch, fall further behind No means of automated recovery Only solvable with good monitoring and recovery procedures Can automate removal from use, but requires cluster management tools

51 failure Load balancers can remove broken or overloaded application reverse proxy caches. Reverse proxy caches like Varnish can automatically use only functional application servers. Cluster management tools like heartbeat2 can manage service IPs on MySQL servers to automate failover. Conclusion: Each layer intelligently monitors and uses the servers beneath it.

52 All content in this presentation, except where noted otherwise, is Creative Commons Attribution- ShareAlike 3.0 licensed and copyright 2009 Four Kitchen Studios, LLC.