Patterns for building resilient software systems - 2019

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© 2018, Amazon Web Services, Inc. or its Affiliates. All rights reserved. Amazon Confidential and Trademark © 2018, Amazon Web Services, Inc. or its Affiliates. All rights reserved. Amazon Confidential and Trademark Adrian Hornsby Sr. Technical Evangelist Amazon Web Services @adhorn Patterns for Building Resilient Software Systems

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. The Famous 9s of availability Availability Downtime per year 99% (2-nines) 3 days 15 hours 99.9% (3-nines) 8 hours 45 minutes 99.99% (4-nines) 52 minutes 99.999% (5-nines) 5 minutes 99.9999% (6-nines) 31 seconds

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Availability in parallel Component Availability Downtime X 99% (2-nines) 3 days 15 hours Two X in parallel 99.99% (4-nines) 52 minutes Three X in parallel 99.9999% (6-nines) 31 seconds

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. AWS Region and availability zones Region Availability zone a Availability zone b Availability zone c data center data center data center data center data center data center data center data center data center n data centers per AZ (1 or more) n AZs per region (typically 3+)

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Pattern 1: Multi-AZ architecture Region Availability zone a Availability zone b Availability zone c Instances Instances Instances DB Instance DB instance standby

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Multi-AZ architecture Region Availability zone a Availability zone b Availability zone c Instances Instances Instances DB Instance DB instance standby X

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Multi-AZ architecture • Enables fault-tolerant applications • AWS regional services designed to withstand AZ failures • Leveraged by most AWS regional services (S3, DynamoDB, ELBs, …)

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Zonal services • Amazon EC2 instances • Amazon EBS volumes • Amazon EMR clusters • AWS CloudHSM instances • NAT gateways • etc. Regional services • Amazon S3 • Amazon DynamoDB • Amazon EFS • Amazon Aurora Serverless • Amazon API Gateway • AWS Fargate • AWS Lambda • Amazon Kinesis • Amazon SQS • Etc.

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. System properties Cell 0 Service Cell 1 Cell n • Workload isolation • Failure containment • Scale-out vs. scale-up • Testability • Manageability X

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Shuffle sharding Nodes = 100 Shard size = 5 Combinations = 75 million! Overlap % customers 0 77% 1 21% 2 1.8% 3 0.06% 4 0.0006% 5 0.0000013%

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Process A Process B Process A Process B Synchronous Asynchronous Waiting Working Continues get or fetch result Get result Pattern 5: Decoupling with async pattern

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. API: {DO foo} PUT JOB: {JobID: 0001, Task: DO foo} API: {JobID: 0001} GET JOB: {JobID: 0001, Task: DO foo} {JobID: 0001, Result: bar} Cache node Worker Instance Worker Instance Queue API Instance API Instance API Instance

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Degrade & prioritize traffic with queues Worker Instance Worker Instance API Instance API Instance API Instance High Priority Queue Low Priority Queue

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Users App DB Conn Pool INSERT INSERT INSERT INSERT What happens if the DB “slows down”? Timeout client side Timeout backend side ? ?

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. User 1 App DB Conn Pool INSERT Timeout client side = 10s Timeout backend side = default = Infinite Retry INSERT Retry INSERT ERROR: Failed to get connection from pool Retry

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http://docs.python-requests.org/en/master/user/advanced/#timeouts

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https://dev.mysql.com/doc/connector-j/5.1/en/connector-j-reference-configuration-properties.html

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. @timeout_decorator.timeout(5, timeout_exception=StopIteration) def timed_get(url): return requests.get(url) https://pypi.org/project/timeout-decorator/

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. How else could we have prevented the error? User 1 DB Conn Pool INSERT Retry INSERT Retry INSERT Retry ERROR: Failed to get connection from pool

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. User 1 DB Conn Pool INSERT Timeout client side = 10s Timeout backend side = 10s Wait 2s before Retry INSERT INSERT Wait 4s before Retry Wait 8s before Retry Wait 16s before Retry Pattern 7: Backing off between retries Releasing connections Backoff

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. No jitter With jitter https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/ Simple Exponential Backoff is not enough: Add Jitter

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Example: add jitter 0-1000ms def get_item(self, url, n=1): MAX_TRIES = 12 try: res = requests.get(url) except: if n > MAX_TRIES: return None n += 1 time.sleep((2 ** n) + (random.randint(0, 1000) / 1000.0)) return self.get_item(url, n) else: return res

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. @backoff.on_exception(backoff.full_jitter, max_time=60) def poll_for_message(queue): return queue.get() https://pypi.org/project/backoff/ As of version 1.2, the default jitter function backoff.full_jitter implements the ‘Full Jitter’ algorithm as defined in the AWS Architecture Blog’s Exponential Backoff And Jitter post.

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Auto Scaling group Service A Availability zone 1 Auto Scaling group AWS Region Service A Availability zone 2 Service B Service B database Email Probing for health Cluster

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Pattern 8: Circuit Breaker • Wrap a protected function call in a circuit breaker object, which monitors for failures. • If failures reach a certain threshold, the circuit breaker trips. Producer Circuit Breaker Consumer Connection Monitoring Timeouts Breaking Circuit

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Database Federation Users DB Products DB Instance Instance Instance DB Instance DB instance read replica DB Instance DB instance read replica

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Database Sharding User ShardID 002345 A 002346 B 002347 C 002348 B 002349 A C B A Instance Instance Instance DB Instance DB instance read replica DB Instance DB instance read replica DB Instance DB instance read replica

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Pattern 9: Read / Write separation DB Instance DB instance read replica DB instance read replica DB instance read replica Instance Instance Instance Supports degradation through Read-Only mode

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. “Chaos Engineering is the discipline of experimenting on a distributed system in order to build confidence in the system’s capability to withstand turbulent conditions in production.” http://principlesofchaos.org

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© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved. Pattern 10: Failure injection • Start small & build confidence • Application level • Host failure • Resource attacks (CPU, memory, …) • Network attacks (dependencies, latency, …) • Region attacks • “Paul” attack

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