RailsTips.org

Exploring Virtual Clusters for Rails Development and Deployment By Bradley Taylor

virtual machine

• behaves like virtual server
• operating system
• many per physical server
• apartment complex
• aka: vps, slice, container, accelerator, vm

shared hardware

• processor (multi-core)
• memory
• storage (RAID)
• network

dedicated resources

• guaranteed memory, storage and cpu usage

why?

• consolidate servers
• isolate applications – helps you avoid shared hosting disaster
• replicate configurations
• utilize all available hardware
• tune resource allocation

isolation

• protect applications from each other
• different operating systems
• different stacks for different apps
• avoid problems of shared hosting
• contain intrusion

replication

• easily create from images
• standardized deployment
• automation

utilization

• fully utilize cpu (mostly idle in web apps, allows apps to share cpu power)
• reclaim unused memory
• reclaim unused storage

resource allocation

• give a server exactly what it needs (smaller memory for svn and such)
• grow/shrink on demand or with a quick reboot
• load balance servers on hardware
• guaranteed vs. burstable (servers can use up to the entire cpu or split if 2 request at the same time)

some numbers

• 40+ host servers => 400+ virtual machines
• 4 data center cabinets
• 256mb to 2gb
• 10gb-100gb storage
• 30-40 per 16

no going back

• powerful
• flexible
• low cost (virtualization is the answer to simple low cost solution)
• rapid
• security

virtual clusters

• multiple virtual servers working together
• shared infrastructure
• application and services layer
• servers are almost “free”

many vs. one

• more than one application, service, customer, version, technology

gains for rails

• development environments (stages)
• memory isolation
• resources to support different traffic
• protect against php/java (a customer survived the front page of digg with mephisto and a 256mb slice)
• acessible multi-server scaling

deployment tools

• subversion – common configuration
• capistrano – automate updates
• rake – stack assembly

virtual cluster examples

production/staging

• two vps
• released and development version
• test changes
• test stack upgrades
• user acceptance

web-app/db/staging

• three vps
• shared database
• ready to scale
• resource tuning

mixed languages

• one vps per technology
• perfect stack
• legacy support
• shared services (db, mail, dns)
• no “dirty” feeling

high availability

• two or more physical servers
• hardware redundancy
• multiple application pairs
• easier shared storage (SAN)
• easier with load balancer

multiple applications

• one server per application
• shared services
• customer isolation
• rapid deployment

specialized roles

• each virtual has a job
• standard: web, app, db
• expanded: mail, ftp, dns, file
• virtual data center: load balancer, firewall

application scaling

• requires foundation
• more cpu
• more memory
• parasite servers

case study: eastmedia

• development (runs off trunk)
• staging (runs off branch)
• production (runs off release tag)
• 2×4gb physical -> 8 virtual

case study: boom design group

• low traffic on some (4 apps per server)
• each high traffic gets own server
• 2gb physical memory -> 9 virtual servers

summary

• application driven
• service driven
• customer driven
• resource pools
• infrastructure (share servers ie: db, etc.)
• less physical servers (so you can be more efficient with resources)