Advanced Deployment

Advanced Deployment Scotland on Rails 2009

Jonathan Weiss, 28 March 2009

Peritor GmbH

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Who am I?

Jonathan Weiss

• Consultant for Peritor GmbH in Berlin

• Specialized in Rails, Scaling, Deployment, and Code Review

• Webistrano - Rails deployment tool

• FreeBSD Rubygems and Ruby on Rails maintainer

http://www.peritor.com

http://blog.innerewut.de

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Deployment

Architecture Process

Deployment

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Deployment Process Requirements

Automatic Reproducible Accountable Notifications

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Deployment Tools

Several tools available

• Capistrano

• Webistrano

• Vlad

• Puppet

• Chef

The deployment process is usually not that complicated

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Architecture

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How deployment starts out …

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… and how it ends

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Agenda

Search

Background Processing

Scaling the database

Multiple Client Installations

Cloud Infrastructure

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General Advice -

Simple is better than complex

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Search

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Search

Full text search

Can become very slow on big data sets

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Full Text Search Engine

Separate Service

• Creates full text index

• Application queries search daemon

• Index update through application or database

Possible Engines

• Ferret

• Sphinx

• Solr

• Lucene

• …

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Search Slave

Database replication slave

• Has complete dataset

• Migrates slow search queries from master

• Can use different database table engine

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Database Index

PostgreSQL Tsearch2

• Core since 8.3

• Allows to create full text index on multiple columns or arbitrary SQL expressions

MySQL MyISAM FULLTEXT index

• Only works with MySQL <= 5.0 and MyISAM tables

• Full text index on multiple columns

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What to use?

Different characteristics

• Real-time updates and stale data

• Lost updates

• Performance

• Document content and format

• Complexity

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Problem

Long running tasks

• Resizing uploaded images

• Mailing

• Computing an expensive operation

• Accessing slow back-ends

When running inside request-response-cycle

• Blocks user

• Blocks Rails instance

• Hard to monitor and debug

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Solution

Asynchronous processing in the background

Message/Queue Scheduler

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Options

Options for message bus:

• Database

• Amazon SQS

• Drb

• Memcache

• ActiveMQ

• …

Options for background process:

• (Ruby) Daemon

• Cron job with script/runner

• Forked process

• Delayed Job / BJ / (Backgroundrb)

• run_later

• ….

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Database/Ruby daemon example

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One database for everything

• All domain data in one place

• The simplest solution

Problems at some point

• Number of read and write requests

• Data size

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Read Slave

• Slave replicates each SQL-statement on the master

• Increase read performance by reading from replicating slave

• Stale read problem

• Better used explicitly, but then makes you think

Better use memcached

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Master-Master

• Increase write and read performance

• Each server is a slave of the other

• Synchronization can be tricky

• Limited by database size

Better for HA than for write performance

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Data Partitioning

Partition on domain models

• Separate users and products

• Makes sense if JOINs are rare

• Scales reads/writes

• Reduces data size per database

• Depends on separate domains

Simple and effective

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Data Partitioning

Sharding

• Split data into shards

• All tables

• Only big ones like users

• Partition by id, hash function or lookup

• Complex and makes JOINs complicated



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Data Partitioning

Sharding

• Split data into shards

• All tables

• Only big ones like users

• Partition by id, hash function or lookup

• Complex and makes JOINs complicated



Last resort

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Alternatives

Data size is often the bigger problem

Reduce data size Archiving

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Archiving

Get rid of (historical) data

• Delete old data

• Aggregate old data

• Partition old data

Have an archiving policy from the start

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Reduce data size

Avoid exponential data growth

• Do not store data in database, move to

• File system

• S3

• SimpleDB

• Do not normalize data

• Duplicate data in order to remove JOINs (and JOIN tables)

• Combine indices

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Multiple clients

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Multiple Clients

NOT the same as multiple users

Client is more like a separate domain – i.e. expansion to another country

• Different settings

• Different themes

• Different features enabled

• Different language

• Different audience

How to combine in one app?

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Multiple Clients

Questions to ask

• How many different clients?

• Is there shared state (users, settings, posts, …)?

• What is the expected data size and growth of each client?

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Multiple Clients

The easy way to maintenance hell

• Fork the code

• One branch per client

• One install per client

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Multiple Clients

Same code – same database

• Move different behavior into configuration

• Move configuration into database

• Scope data by DB-column

• Scope all data request in the code

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Multiple Clients

Same code – partition the data


• Partition data by database

Hardcode database while booting

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Multiple Clients

Same code – partition the data


• Partition data by database

Choose database dynamically

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Multiple Clients

Generate local databases

• Import global content into master DB

• Push shared content in the correct format to app DBs

• Build reverse channel if needed

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Servers come and go

• You do not know your servers before deploying

• Restarting is the same as introducing a new machine

You can’t hardcode IPs

database.yml

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Solution #1

Query and manually adjust

• Servers do not change that often

• New nodes probably need manual intervention

• Use AWS ElasticIPs to ease the pain

Set servers dynamically AWS Elastic IP

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Solution #2

Use a central directory service

• A central place to manage your running instances

• Instances query the directory and react

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Solution #2

Use a central directory service

• A central place to manage your running instances

• Instances query the directory and react

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Central Directory

Different Implementations

• File on S3

• SimpleDB

• A complete service, capable of monitoring and controlling your instances

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Summary

Simple is better than complex

Carefully evaluate the different solutions

Only introduce a new component if you really need to

Everything has strings attached

Solving the data size problem often solves others too

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Questions?

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Peritor GmbH

Teutonenstraße 16 14129 Berlin

Telefon: +49 (0)30 69 20 09 84 0 Telefax: +49 (0)30 69 20 09 84 9

Internet: www.peritor.com E-Mail: [email protected]

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Advanced Deployment

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Advanced Deployment