Web Architectures and Hosting (GAE and more)

1. Web ArchitecturesandHosting (GAE and more) Willem VisserRW334

2. 3-Layered Architecture • Presentation Layer • HTML, etc. • Application/Logic Layer • Persistence/Data Layer • Linear interaction • Tier versus layered • Layers are logical whereas tiers are physical

3. Two Related Concepts • Logical approaches to the architecture • Model-View-Controller (MVC) • Model-View-Presenter (MVP) • MVC != MVP != 3-Layered

4. Model View Controller • Every action in the View has a counterpart in the Controller • View is stateless • This is how we typically develop request db query Browser Controller Model response db data guicontent data View

5. Model View Presenter • Every action in the View has a counterpart in the Controller, but no direct coupling, rather interface to allow mocking the View • View is stateless and no direct connection to Model • Makes testing simpler data request db query Browser View Presenter Model response db data data

6. Typical Physical Setup Server DB Cache Server CDN shared memcache Internet Load Balancer Cache DB Server Cache

7. AppEngine • Run your web app on Google’s infrastructure • Platform as a Service (PaaS) • Takes the stress out of hosting your app • Scales automatically • No servers to maintain • Can direct any URL to your app, or, use a free domain on appspot.com • Free up to a point • Quotas to ensure fairness http://code.google.com/appengine/docs/whatisgoogleappengine.html

8. Languages Supported • Initially only Python • Now also JVM-based languages • Java first and foremost • Also Scala, etc. • Eclipse plugin • GWT and GAE • We will only consider Python

9. What you get • dynamic web serving, with full support for common web technologies • persistent storage with queries, sorting and transactions • automatic scaling and load balancing • APIs for authenticating users and sending email using Google Accounts • a fully featured local development environment that simulates Google App Engine on your computer • task queues for performing work outside of the scope of a web request • scheduled tasks for triggering events at specified times and regular intervals

10. Sandbox • Apps run in a restricted environment where it has controlled interaction with the underlying operating system • This allows migration to various servers • Limitations • Apps can only speak to the server through http(s) • Server can only communicate to the outside via URL Fetch and Email • Storage is only via provided services such as Datastore and Memcache, no files can be written and can only be read if uploaded with the app • Code only runs if invoked by a request, must finish within 30s and cannot continue after the response is sent

11. Java Runtime Environment • Java servlets • Must stay within sandbox, no opening sockets for example • Supports Java Data Objects (JDO) and Java Persistence API (JPA) for data storage • Java Mail API for interaction with the Mail Service • Multi-threaded with restrictions

12. Datastore • Distributed data storage • Data Objects as Entities • Kind • Set of properties • Schemaless • Application enforces the structure • Transactions • Fail or all pass • Will retry if concurrently being updated • Entity Groups • Application assign it when entity is created • Entities from the same group are stored together • Transactions manipulate data in a single group

13. Two types of Datastores • Master/Slave • Default • Writes data to other data center (Slave) • Consistency • Not availability • Low Storage and CPU costs • High Replication • Replicated over several data centers using Paxos Algorithm • High availability • Even during planned outage • Higher latency for writes • Entity groups very important now • 3x the storage and CPU Deprecated 4 April 2012

14. One Type of Datastore • High Replication • Replicated over several data centers using Paxos Algorithm • High availability • Even during planned outage • Higher latency for writes

15. Cloud SQL • MySQL in the Cloud • Not Free anymore! • Some minor restrictions

16. Google Accounts • Use Google Account information during authentication • Makes it easy to add access control to your app • OpenID is supported since May 2010 (1.3.4)

17. Services • URL Fetch • Allows you to access webpages • Mail • Memcache • High performance in-memory key-value store • Image • Crop, resize, rotate and flip JPEG and PNG formats • Scheduled Tasks • Task Queues

18. Quotas • Free accounts • 1Gb of static storage (Code) • 1GB each for incoming and outgoing data • 10 applications per developer account • Billable versus Fixed Quotas • Fixed quotas enforce architecture boundaries • Billable quotas are set by the application developer • Detailed information is found here: • https://developers.google.com/appengine/docs/quotas

19. GAE Verdict • Pros • Cheap and easy to use • Good integration with other Google services • SQL support (at a price) • Cons • Not “real” Java • Very deep sandbox, with very many limitations • Limited Multi-threading • BigTable • Weak queries, hard to import/export data • Scalability, but not performance • 100 or 100M users and system perform equally slow

20. Amazon Elastic Beanstalk • Apache Tomcat on top of EC2 (IaaS) • Pros • No limitations on threading, file and network IO • Lots of Storage options • NoSQL, Relational (Relational Database Service), Your Own • Good integration with Amazon services • Cons • Price! • Nice for large deployments but too much for the little guy • However do have Free options now as well

21. CloudBees RUN@Cloud • Also based on EC2 and Tomcat • Automated version of Beanstalk+RDS • Will have other back-ends in future • Pros • Sticky session management, unlike Beanstalk • Multiple Tomcat servers per EC2 • Lower cost and in fact have free option • Native support for MySQL • Access to all Amazon services but also DEV@Cloud • Continuous Build, Integration and Testing in the Cloud • Cons • Like GAE, will swap out inactive JVMs