Accelerating Rails with edge caching

Accelerating Rails
with edge caching
Michael May | @ohaimmay | SFRails | 10/16/2014

Topic
• Rails caching best practices
• Dynamic content/caching
• Edge caching
• Edge caching dynamic content with Rails

Rails caching
• Query/SQL
• Page/Action (removed from Rails 4 core)
• Asset
• Fragment

Rails caching
config.action_controller.perform_caching = true

Query caching
• Automagically done by rails when
perform_caching = true
• Not cached between requests!
• Could just store the query result in a variable

Manual Query Caching
class Product < MyModel
def self.out_of_stock
Rails.cache.fetch("out_of_stock", expires_in: 1.hour) do
Product.where("inventory.quantity = 0")
end
end
end

Asset Caching
• Serve static assets from a proxy
• config.serve_static_assets = false
• Enable Compression*
• config.assets.compress = true
• # In Rails 4
• config.assets.css_compressor = :yui
• config.assets.js_compressor = :uglifier
• Asset Digests
• config.assets.digest = true

mmay.rocks/assets/catzlol-75408509152249b79b818b252da51bc4.

Enable Compression*
Compress HTML, JSON responses at runtime
module FastestAppEver
class Application < Rails::Application
config.middleware.use Rack::Deflater
end
* http://robots.thoughtbot.com/content-compression-with-rack-deflater
end

Asset Caching
• Configure an asset host if needed
• config.action_controller.asset_host =
ENV[‘FASTLY_CDN_URL']
• Cache-Control like a pro
• config.static_cache_control = 'public, s-maxage=
15552000, maxage=2592000'

Cache-Control
public, s-maxage=15552000, maxage=2592000
public
“please cache me”
maxage=2592000
“keep me for 30 days”
s-maxage=15552000
“PROXIES ONLY! - Keep me for 180 days”

Keepin’ it fresh
• stale-while-revalidate
• Serve the current (stale) version for n seconds while it re-fetches the
latest version in the background
• Cache-Control: max-age=604800, stale-while-revalidate=86400
• stale-if-error
• If the re-fetch fails within n seconds of the response becoming stale,
serve the cached response
• Cache-Control: max-age=604800, stale-while-revalidate=86400, stale-if-error=
259200

The Vary HTTP Header
• In general, never Vary on anything other than
Content-Encoding
• Varying makes it impossible to serve the same
response more than once and limits caching
benefits
• NEVER Vary on User-Agent!
• There are THOUSANDS of these!

Dynamic Content
• Changes are unpredictable!
• user driven events
• Can’t just set a Time To Live (TTL)

Dynamic Content
• Changes are unpredictable!
• user driven events
• Can’t just set a Time To Live (TTL)
• Frequently, but not continuously changing
• Actually static for short periods of time (we can
cache static things)!

Dynamic Content Caching
• Usually don’t
• Edge Side Includes (ESI)
• Dynamic Site Acceleration (DSA)

Fragment Caching
The rails answer to caching dynamic HTML
# products/index.html.erb
<% cache(cache_key_for_products) do %>
<% Product.all.each do |p| %>
<%= link_to p.name, product_url(p) %>
<% end %>
<% end %>
# products_controller.rb
def update
…
expire_fragment(cache_key_for_products)
…
end

Nested Fragment Caching
<% cache(cache_key_for_products) do %>
All available products:
<% Product.all.each do |p| %>
<% cache(p) do %>
<%= link_to p.name, product_url(p) %>
<% end %>
<% end %>
<% end %>

Nested Fragment Issues
• Tedious
• Comb through (probably terrible) view code
• Cache keys are weird
• “A given key should always return the same content.” - DHH
• products/15-20110218104500
• “A given key should always return the most up-to-date content.” - Me
• products/15
• Hacks around cache limitations
• Memcache has no wildcard purging!

Nested Fragment Issues
• Garbage left in the cache
• Defaults writing to disk
• Memcached, Redis, etc
• Probably lives in the same DC as your app server
• Distributing, replication takes effort
• What about dynamic API caching?
• “The caching itself happens in the views based on partials rendering
the objects in question”
• Take control over your cached data!

Edge Caching
aka content delivery network
aka CDN

Edge Cache
• Geographically distributed
• Highly optimized storage and network
(nanoseconds count)
• Move content physically closer to the end-users
• End goal - DECREASE LATENCY!

The more content we
can offload, the better
performance we get

#cachemoney
• App servers cost real cash money (not cache
money)
• Less requests back to your application server
• Avoid complex or less efficient strategies
• Edge Side Includes (ESI)
• Fragment caching

Edge caching the
dynamic content

Our approach to dynamic
content
• Tag content with Surrogate-Key HTTP headers
• Programmatically purge (~150ms globally)
• By Surrogate-Key
• By resource path
• Real-time analytics and log streaming
• Optimize the hell out of the pieces of the network we
can control

Tagging responses
with Surrogate-Key

class ProductsController < ApplicationController
# set Cache-Control, strip Set-Cookie
before_filter :set_cache_control_headers,only [:index,:show]
def index
@products = Product.last(10)
# set Surrogate-Key: products
set_surrogate_key_header @products.table_key
respond_with @products
end
def show
@product = Products.find(params[:id])
# set Surrogate-Key: product/666
set_surrogate_key_header @product.record_key
respond_with @product
end
end

class ProductsController < ApplicationController
def create
@product = Product.new(params)
if @product.save
# purge Surrogate-Key: products
@product.purge_all
render @product
end
end
...

def update
@product = Product.find(params[:id])
if @product.update(params)
# purge Surrogate-Key: product/666
@product.purge
render @product
end
end

fastly-rails
github.com/fastly/fastly-rails

Be aware of cookies
• Nothing with a Set-Cookie header is cached (by
default)
• Authentication frameworks/middleware might
inject Set-Cookie after the rails stack removes it
• Avoid caching pains by knowing when, where,
and how you use Set-Cookie

URL Rewriting
• Apache, nginx, etc support URL Rewriting
• Filter bad requests
• Normalize paths

URL Rewrite at the edge
• Varnish HTTP cache
• VCL
• Requests never hit origin!

What can we do better?
• Add better caching defaults?
• Cache-Control, stale-while-revalidate, stale-if-error
• Re-use existing rails cache interfaces for edge
caching?
• ActiveSupport::Cache::EdgeStore
• More fine-grained integration with HTTP accelerators
like Varnish?

Takeaways
• Rails has tons of built-in caching options
• Get fancy with Cache-Control directives
• Use Google PageSpeed Insights (chrome plugin
adds it to dev tools)
• Dynamic edge caching is all about the power of
purge!
• Similar school of thought to rails action caching

Questions?
Contact: Michael May | @ohaimmay | michael@fastly.com
cool links:
fastly-rails - github.com/fastly/fastly-rails
surrogate keys - fastly.com/blog/surrogate-keys-part-1
cache-control tutorial - docs.fastly.com/guides/tutorials/cache-control-tutorial
serve stale cache-control - fastly.com/blog/stale-while-revalidate
vary header best practices - fastly.com/blog/best-practices-for-using-the-vary-header
caching like & share buttons - fastly.com/blog/caching-like-and-share-buttons
pagespeed insights - developers.google.com/speed/pagespeed

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