Scalable webapps

We won't talk about

• Clean Code
• Language of choice
• Colour of your IDE..
• Absolute truths
• Complex code

We'll talk about

• My personal experiences
• How systems where scale >= 1 can fail spectacularly
• How you'll fail spectacularly
• Actually useful stuff :)

Scalable?

• No local state
• distributed (if needed)
• decoupled components
• Service discovery
• Fail gracefully (No 500 pages pls)

Session?

• Yes please!
• Store on local disk! (it works in the beginning)
• Hm... Let's scale up!
• DAFUQ??
• Common session store for all instances!
• Profit!

Static assets

• simply write the uploaded file to disk
• Ok, but what if we are flickr?
• Buy more disks (No)
• Run multiple instances of the same service
• 404????
• Shared storage!
• Buy more disks for your shared storage :)

Long running operations?

• It'll be less than http request timeout
• ....
• maybe
• what if not?
• * Empty reply from server
  * Connection #0 to host localhost left intact
  curl: (52) Empty reply from server
   :(((
• Use queues 
• Poll for the result!
• If we fail we can still retry 
• Micro services are cool anyway

Loadbalancer what?

• Actual examples
• Algorithms (RR, WRR, WTF) 
• Loadbalancers in the wild