Patterns for resilient architecture & optimizing web performance
Tags: todayilearned, architecture, webperf, serverless
Published: 2020-02-03 13:00:20

*TL;DR notes from articles I read today.*

### [Patterns for resilient architecture: Embracing failure at scale](http://bit.ly/38YQm8P)

- Build your application to be redundant, duplicating components to increase overall availability across multiple availability zones or even regions. To support this, ensure you have a stateless application and perhaps an elastic load balancer to distribute requests.
- Enable auto-scaling not just for AWS services but application auto-scaling for any service built on AWS. Determine your auto-scaling technology by the speed you tolerate - preconfigure custom golden AMIs, avoid running or configuring at startup time, replace configuration scripts with Dockerfiles, or use container platforms like ECS or Lambda functions.
- Use infrastructure as code for repeatability, knowledge sharing, and history preservation and have an immutable infrastructure with immutable components replaced for every deployment, with no updates on live systems and always starting with a new instance of every resource, with an immutable server pattern. 
- As a stateless service, treat all client requests independently of prior requests and sessions, storing no information in local memory. Share state with any resources within the auto-scaling group using in-memory object caching systems or distributed databases. 

*[Full post here](http://bit.ly/38YQm8P), 10 mins read*

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###[Tips to speed up serverless web apps in AWS](http://bit.ly/384p1li)

- Keep Lambda functions warm by invoking the Ping function using AWS CloudWatch or Lambda with Scheduled Events and using the Serverless WarmUP plugin.
- Avoid cross-origin resource sharing (CORS) by accessing your API and frontend using the same origin point. Set origin protocol policy to HTTPS when connecting the API gateway to AWS CloudFront and configure both API Gateway and CloudFront to the same domain, and configure their routing accordingly.
- Deploy API gateways as REGIONAL endpoints.
- Optimize the frontend by compressing files such as JavaScript, CSS using GZIP, Upload to S3. Use the correct Content-Encoding: gzip headers, and enable Compress Objects Automatically in CloudFront.
- Use the appropriate memory for Lambda functions. Increase CPU speed when using smaller memory for Lambda. 

*[Full post here](http://bit.ly/384p1li), 4 mins read*

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### [Optimizing website performance and critical rendering path](http://bit.ly/36Nrcbz)

- Many things can lead to high rendering times for web pages - the amount of data transferred, the number of resources to download, length of the critical rendering path (CRP), etc. 
- To minimize data transferred, remove unused parts (unreachable JavaScript functions, styles with selectors not matching any element, HTML tags always hidden with CSS) and remove all duplicates.
- Reduce the total count of critical resources to download by setting media attributes for all links referencing stylesheets and making some styles inlined. Also, mark all script tags as async (not parser blocking) or defer (evaluated at end of page load).
- You can shorten the CRP with the approaches above, and also rearrange the code amongst files so that the styles and scripts of above-the-fold content load before you parse or render anything else.
- Keep style tags and script tags close to each other in HTML (linewise) to help the browser preloader, and batch HTML updates to avoid multiple layout changes (such as those triggered by window resizing or device orientation).

*[Full post here](http://bit.ly/36Nrcbz), 8 mins read*

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