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update entry on SQS

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Thomas Bishop 2024-11-22 15:34:57 +00:00
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zk/Messaging_services.md
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@ -4,21 +4,6 @@ tags: [AWS]
# AWS Messaging services
## SQS
> SQS: Simple Queue Service
SQS is a service that allows you to send, store and receive messages between
apps and software components built in AWS, with automatic encryption. It helps
with decoupling and scaling.
As the name indicates, its operating mode is that of a
[queue](Queue.md) data structure offering first-in, first-out
and other queue implementations.
An example application of this would be to set up an SQS queue that receives
messages and triggers a lambda whenever a new message is added.
## SNS
> SNS: Simple Notification Service
@ -30,3 +15,5 @@ through SMS, text, push notifications and email.
**SNS pushes messages out to subscribers while SQS stores the messages until
someone reads them.**
Relation between SNS and SQS - typically paired aren't they.

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zk/SQS.md Normal file
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---
tags: [AWS, SQS]
---
# AWS SQS
SQS ("Simple Queue Service") is a service that allows you to send, store and
receive messages between apps and software components built in AWS. It helps
with decoupling and scaling.
> Amazon SQS is a distributed queue system that enables web service applications
> to quickly and reliably queue messages that one component in the application
> generates to be consumed by another component where a queue is a temporary
> repository for messages that are awaiting processing.
As the name indicates, its operating mode is that of a [queue](Queue.md) data
structure offering first-in, first-out and other queue implementations.
## Example use case
![SQS example diagram](../img/SQS-example.png)
A request is made to an [API Gateway](API_Gateway.md) endpoint with a body. The
body is then parsed and inserted into a database.
The benefit of adding SQS as a buffer between the request and the updating of
the database:
- It can better handle spikes in activity, buffering requests to the database
until it is ready to handle them. This prevents the messages getting lost if
the server is overloaded
- There is a retry mechanism built into SQS. If the database write fails, the
message stays in the queue allowing for retries
- It facilitates decoupling. Without SQS as the middleman the responsibilites of
the lambda would be compounded - it would receive requests and update the DB,
plus any additional processes such sending a message to SNS. In the solution
we have two lambdas co-ordinating actions in a decouped manner via SQS.
## Dead letters
As SQS allows for multiple retries we could end up in a situation where a
malformed message is continually processed in a loop. To avoid this you can set
a maxiumum retry limit and, when this is exceeded, shift the problematic message
to the dead letter queue (DLQ) and remove it from the main queue.
![SQS deadletter example](../img/SQS-deadletter.png)
If the DLQ reaches a certain threshold this can trigger additional handling such
as raising an Alert in [CloudWatch](./AWS_CloudWatch.md) or other monitoring
tool.