Are you considering using AWS Lambda with your RDS/RDBMS solutions, but don’t know where to start? In this session, we look at recommended architectural patterns and best practices around using RDS/RDBMS solutions with Lambda functions. We also discuss migration steps, covering migration from on-premises RDBMS solutions to AWS serverless infrastructure (keeping the same RDBMS application model). Come and join our discussion, ask questions, and learn more about using Lambda with RDS/RDBMS solutions.

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AWS re:INVENT
Best Practices for Using AWS
Lambda with RDS/RDBMS Solutions
M a y a n k T h a k k a r , H C L S S o l u t i o n s A r c h i t e c t
E m m a Z h a o , S o f t w a r e D e v e l o p m e n t M a n a g e r , L a m b d a
D e c e m b e r 1 , 2 0 1 7
S R V 3 2 0

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Problem: Managing database connections
…
AWS Lambda can scale, can your database connections?
Is connection pooling
the answer?

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Lambda: The scaling background

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Time
Container A
Container B
Container C
Container D
Lambda—scaling

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How does that affect connection pooling?

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Connection pooling with Lambda
• Only one connection is used at a time in a
container
• Connection pool size = 1
• Just initialize a connection object in the
global section of Lambda and use that
connection
OR

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Connection pooling with Lambda —challenges
• No hook to indicate destruction of Lambda containers
• Cannot explicitly close connections when the container is
recycled
• Fall back on database TTL to clean up connections
• No control over lifecycle of Lambda containers
• Can result in many connections sitting idle
• Different containers for different Lambda functions
• No reuse of connections across Lambda functions

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Managing concurrency

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Solution 1
Set concurrency limits

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Solution 1a: Account concurrency limit
Use AWS Organizations to manage your accounts
AWS account
Lambda can help
with retries of
throttled
invocations*
*Refer to references section for details

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Solution 1b: Function concurrency limit
Lambda can help
with retries of
throttled
invocations*
*Refer to references section for details

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Concurrency limits—benefits
• Lambda concurrency limit can be set at the
account level or at the function level
• Simple to set up
• Account level limit requires AWS support
• AWS Lambda manages retries for throttled
invocations*

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Concurrency limits—challenges
• Account level limit:
• Covers Lambdas across the account—difficult to isolate DB
interfacing functions
• Possibility of accounts sprawl
• Function level limit:
• Prior knowledge of DB accessing functions required
• Limit should correspond to peak concurrency—prior
application behavior knowledge required
• Cannot spread out connections dynamically because load
across Lambdas varies

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Solution 2
Dynamic connection management
c u s t o m s o l u t i o n

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Dynamic connection management
Amazon DynamoDB
Helper
Maintain atomic counter
and max count
Open/close
connections
DB operations
Amazon CloudWatch
CloudWatch AlarmDo something interesting

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Dynamic connection management
Demo

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Benefits
• Scalable solution: depends on Lambda and DynamoDB
• Connections count managed from DB perspective
• No limit on number of Lambda functions
• Can spread DB connections across Lambda functions at runtime
• Eliminate choke points and better serve hotspots
• Easy update: control usable connections count through
DynamoDB
• Use published CloudWatch metrics to react to out-of-connection
errors

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Challenges
• No retries of throttled invocations: requires custom
solution
• More resources to manage
• No connection reuse
• Slightly increased latency

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Summary
• Lambda scaling model and connection pooling do
not mix
• Use a single connection, initialized in the global section
• Manage concurrency using:
• Account and function level concurrency Limits
• Custom solution: dynamic connection management

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References
• AWS organizations
• https://aws.amazon.com/organizations/
• AWS serverless :
• https://aws.amazon.com/serverless/
• AWS Lambda container reuse:
• https://aws.amazon.com/blogs/compute/container-reuse-in-lambda/
• Lambda—retries of throttled invocations:
• http://docs.aws.amazon.com/lambda/latest/dg/concurrent-
executions.html#concurrent-execution-safety-limit
• Dynamic connections manager sample code:
• https://github.com/awslabs/LambdaRDS-ManageConnections

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Questions

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Thank you!