Agenda Design Considerations in moving to Cloud Introduction to Windows Azure Demo
Business Benefits of Cloud Computing Almost zero upfront infrastructure investment. Just-in-time infrastructure. More efficient resource utilization. Usage based costing. Reduced time to Market.
Challenges Faced by Apps in theCloud Application Scalability Cloud promises rapid (de)provisioning of resources. How do you tap into that to create scalable systems? Application Availability Underlying resource failures happen … usually more frequently than in traditional data centers. How do you overcome that to create highly available systems?
The Scalability Challenge Two different components to scale: State (inputs, data store, output) Behavior (business logic) Any non-trivial application has both. Scaling one component means scaling the other, too.
Scalability Considerations Performance vs Scalability Latency vs Throughput Availability vs ConsistencyHow do you manage overload ?
Scalable Service A scalable architecture is critical to take advantage of scalable infrastructure. Characteristic of Scalable Service: Increasing resources results in a proportional increase in performance A scalable service is capable of handling heterogeneity A scalable service is operationally efficient A scalable service is resilient A scalable service becomes more cost effective when it grows.
1. Design for Failure and nothing will really fail Avoid single points of failure Assume everything fails and design backwards. Applications should continue to function even if the physical hardware fails or removed or replaced.
Design for Failure contd.. Unit of failure is a single host Where possible, choose services and infrastructure that assume host failures happen. By building simple services composed of a single host, rather then multiple dependent hosts, one can create replicated service instances that can survive host failures. Make your services small and stateless. Relax consistency requirements.
2. Build Loosely Coupled SystemsThe looser they’re coupled, the bigger they scale Loosely Coupled Dependencies Avoid complex design and interactions. Best Practices: Tiered Architecture Scale out units Single role
3. Implement ElasticityElasticity is fundamental property of cloud Ability to add and remove capacity as and when it is required. Use Elastic Load Balancing. Use Auto-Scaling (free)
4. Build Security in every layerDesign with security in mind Encrypt data at rest. Encrypt data at transit (SSL) Consider encrypted file system for sensitive data. Rotate your credentials, Pass in arguments encrypted. Use MultiFactor authentication. Restrict external access to specific IP ranges.
5. Don’t Fear ConstraintsRe-think architectural constraints More RAM? – Distribute load across machines. Shared distributed cache. Better IOPS on database – Multiple read-only / Sharding. Performance – Caching at different levels
6. Think ParallelSerial and Sequential is now history Experiment different architectures in parallel Multi-threading and Concurrent requests to cloud services. Run parallel Map Reduce Jobs Use Elastic Load balancing to distribute load across multiple servers. Decompose job into its simplest form – and with “Shared Nothing”
7. Leverage many storage optionsOne Size does not fit all Amazon S3 / Azure Blob – Large Static Objects Amazon Simple DB / Azure Tables – Data indexing and Querying Amazon RDS / SQL Azure – RDMBS Service – Automated and Managed MySQL/Azure Amazon Cloud Front / Azure CDN – Content Distribution
Cloud Architecture Lessons Design for failure and nothing fails. Loose coupling sets you free. Implement Elasticity. Build Security in every layer. Don’t fear constraints. Think Parallel. Leverage many storage options.
The Availability Challenge Availability: Tolerate failures Traditional IT focuses on increasing MTTF Mean Time to Failure Cloud IT focuses on reducing MTTR Mean Time to Recovery
Data modelling Classic distributed systems focused on ACID semantics Atomicity: either the operation (e.g., write) is performed on all replicas or is not performed on any of them Consistency: after each operation all replicas reach the same state Isolation: no operation (e.g., read) can see the data from another operation (e.g., write) in an intermediate state Durability: once a write has been successful, that write will persist indefinitely Modern Internet Systems – focused on BASE Basically Available Soft-state (or scalable) Eventually consistent
CAP TheoremAny distributed system has three properties – CAP Strong Consistency: all clients see the same view, even in the presence of updates High Availability: all clients can find some replica of the data, even in the presence of failures Partition-tolerance: the system properties hold even when the system is partitionedAs per CAP theorem you can only have two of these three properties. Choiceof which feature to discard determines the nature of your system.
Map Reduce Model for processing large data sets. Many tasks composed of processing lots of data to produce lots of other data Want to use hundreds or thousands of CPUs... but this needs to be easy! Contains Map and Reduce functions.
Programming model Input & Output: each a set of key/value pairs Programmer specifies two functions: map (in_key, in_value) -> list(out_key, intermediate_value) Processes input key/value pair Produces set of intermediate pairs reduce (out_key, list(intermediate_value)) -> list(out_value) Combines all intermediate values for a particular key Produces a set of merged output values (usually just one)