Scaling Web Applications with Background
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Presented at All Things Open 2023 Presented by Lydia Cupery - HubSpot Title: Scaling Web Applications with Background Jobs: Takeaways from Generating a Huge PDF Abstract: Do you need to perform time-consuming or CPU-intensive processes in your web application but are concerned about performance? That’s where background jobs come in. By offloading resource-intensive tasks to separate worker processes, you can improve the scalability of your web application. In this talk, I'll share my experience of using background jobs to scale our web application. I'll discuss the challenges my team faced that led us to adopt background jobs. Then, I'll share practical tips on how to design background jobs for CPU-intensive or time-consuming processes, such as generating huge PDFs and batch emailing. I'll wrap up by going over the performance and cost tradeoffs of background jobs. I'll use Typescript, Express, and Heroku as examples in this talk, but the concepts and best practices that I'll share are applicable to other languages and tools. Find more info about All Things Open: On the web: https://www.allthingsopen.org/ Twitter: https://twitter.com/AllThingsOpen LinkedIn: https://www.linkedin.com/company/all-things-open/ Instagram: https://www.instagram.com/allthingsopen/ Facebook: https://www.facebook.com/AllThingsOpen Mastodon: https://mastodon.social/@allthingsopen Threads: https://www.threads.net/@allthingsopen 2023 conference: https://2023.allthingsopen.org/
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Scaling Web Applications with Background
- 1. Scaling Web Applications with Background Jobs: Takeaways from Generating a Huge PDF Lydia Cupery All Things Open, 2023
- 2. Hi! Nice to meet you Lydia Cupery lydia-cupery.com Lydia Cupery
- 3. The Problem
- 5. Motion design Physical Computing Download Invoices Fetch the invoice data from the database Transform data to shape of PDF data Put completed PDF somewhere client can access Write the Invoice PDF for each customer Combine all Invoice PDFs SERVER write customer invoices PDF reference to created PDF CLIENT
- 7. Fetch the invoice data from the database Transform data Put completed PDF somewhere client can access Write the Invoice PDF for each customer Combine all Invoice PDFs
- 8. Write the Invoice PDF for each customer Combine all Invoice PDFs
- 9. First attempt - create one large PDF. Write each customer statement to the main pdf. It works but it takes way too long.
- 10. Okay, what if we create all the PDFs at the same time? And then merge them? We’ll use a Promise.all and store all the individual PDFs in memory.
- 11. What if we processed two or three invoices at a time, and write each of those as pdfs to the file system? Then, we could merge those PDFs together with pdf-lib.
- 12. What if we used an external service? Is there any external service that could help us out with our bottlenecks? Write the Invoice PDF for each customer Combine all Invoice PDFs …perhaps for combining PDFs!
- 13. Cuts down on the time to combine PDFs, but generating the individual PDFs and writing the PDFs to the file system still takes too long.
- 14. Takes Too Long Generating & writing PDFs to the file systems takes too long. Generate too many pdfs in parallel, use a lot of memory, the dyno runs out of memory. Uses Too Much Memory VS
- 15. What if we keep increasing memory, and upgrade our dynos to ones with more memory? invoice report please! report.pdf
- 16. The system could still run out of memory and start failing as soon as more than one user tries to generate a PDF at once. invoice report please! invoice report please! ERROR please load X page! ERROR report.pdf
- 17. Make it a Background Job!
- 18. “Background jobs can dramatically improve the scalability of a web app by enabling it to offload slow or CPU-intensive tasks from its front-end.”
- 19. Browser Web Server Background Service request invoices PDF schedule generate invoice PDF in-progress generate invoice PDF is it done yet? nope! is it done yet? nope! is it done yet? yes! here it is
- 21. web process (web dyno) data store (redis) library to implement queue system on top of redis (BullMQ) worker processes (worker dynos)
- 22. With a Background Job You Can…
- 23. With background jobs you can… Speed Things Up
- 24. Browser Web Server Background Service request invoices PDF schedule generate invoice PDF in-progress generate invoice PDF is it done yet? nope! is it done yet? nope! is it done yet? yes! here it is
- 25. Sorted Customers with Invoices fetch invoice data generate invoices customerIds: A-E fetch invoice data generate invoices customerIds: F-O fetch invoice data generate invoices customerIds: P-Z combine generated invoices JOB QUEUE customers A-E customers F-O customers P-Z customer list/ WORKER_COUNT
- 26. generate invoices customerIds: A-E generate invoices customerIds: F-O generate invoices customerIds: P-Z combine generated invoices JOB QUEUE fetch data (A-E) write invoices upload “batch invoices xxx - 1” fetch data (F-O) write invoices upload “batch invoices xxx - 2” fetch data (P-Z) write invoices upload “batch invoices xxx - 3” combine s3 files to “batch invoices xxx” upload “batch invoices xxx”
- 27. Job Partial Job Partial Job Partial Job Combine Partial Job Outputs output output output
- 28. With background jobs you can… Show Progress
- 29. Progress Indication With no background job (assuming the server doesn’t time out or run out of memory) : Browser Web Server request invoice PDF here it is! generate pdf…
- 31. Browser Web Server Background Service request invoices PDF schedule generate invoice PDF in-progress generate invoice PDF jobs is it done yet? nope! 30% there is it done yet? nope! 70% there is it done yet? yes! here it is
- 32. Generate Partial Invoices Job (input, updateProgress) => ● fetch data to generate invoices ● updateProgress(0.1) JOB PROGRESS 1 .1
- 33. Generate Invoices Job (input, updateProgress) => ● fetch data to generate invoices ● updateProgress(0.1) ● generate the invoices ○ updateProgress each time an invoice generated JOB PROGRESS 1 .2
- 34. Generate Invoices Job (input, updateProgress) => ● fetch data to generate invoices ● updateProgress(0.1) ● generate the invoices ○ updateProgress each time an invoice generated JOB PROGRESS 1 .4
- 35. Generate Invoices Job (input, updateProgress) => ● fetch data to generate invoices ● updateProgress(0.1) ● generate the invoices ○ updateProgress each time an invoice generated JOB PROGRESS 1 .6
- 36. Generate Invoices Job (input, updateProgress) => ● fetch data to generate invoices ● updateProgress(0.1) ● generate the invoices ○ updateProgress each time an invoice generated JOB PROGRESS 1 .8
- 37. Generate Invoices Job (input, updateProgress) => ● fetch data to generate invoices ● updateProgress(0.1) ● generate the invoices ○ updateProgress each time an invoice generated ● updateProgress(0.9) JOB PROGRESS 1 .9
- 38. Generate Invoices Job (input, updateProgress) => ● fetch data to generate invoices ● updateProgress(0.1) ● generate the invoices ○ updateProgress each time an invoice generated ● updateProgress(0.9) ● upload generated file to s3 ● updateProgress(1) JOB PROGRESS 1 1
- 39. view job progress updateProgress(X) updates job progress aggregate progress across jobs requests job progress
- 40. With background jobs you can… Support Simultaneous Users
- 41. Before background jobs… invoice report please! invoice report please! ERROR please load X page! ERROR report.pdf
- 42. invoice report please! please load X page! working on that! progress? progress? invoice report please! working on that! progress? here you go!
- 43. With background jobs you can… Save Jobs for Later
- 44. invoice report please! working on that! progress? progress? invoice report please! working on that! progress?
- 45. With background jobs you can… Have Less Timeouts/Errors
- 46. Communicating with an External Service With no background job: Browser Web Server send out customer emails, please! TIMEOUT ��🏻♀ Mailgun send these emails, please! ��
- 47. Browser Web Server send out customer emails, please! send these emails, please! in-progress Mailgun is it done yet? nope! 30% there is it done yet? nope! 70% there is it done yet? yes - all emails are sent! �� Background Service send these emails, please!
- 48. Recap - With a background job you can… speed things up show progress support simultaneous users have less timeouts/errors save jobs for later
- 49. Should you use a background job?
- 50. You might want a background job for… CPU-intensive jobs Jobs communicating externally I/O intensive jobs Scheduled jobs
- 51. Tips
- 52. Struggling with app responsiveness? Try a background job.
- 53. Don’t recreate the wheel. Use a library with a robust queueing system.
- 54. Does speed matter? It probably does. Parallelize.
- 55. The job queue makes it easy to show users progress. Do so!
- 56. Find the optimal number of workers and optimal amount of resources per worker(see next slide…)
- 57. 1X 1X 1X $25 x 6 = $150 512 MB x 6 = 3GB $50 x 3 = $150 1 GB x 3 3GB 1X 1X 1X 2X 2X 2X $250 x 1 = $250 2.5 GB x 1 = 2.5 GB Perf M
- 58. What about the PDF?
- 59. Fetch the invoice data from the database Transform data to shape of PDF data Put completed PDF somewhere client can access Write the Invoice PDF for each customer Combine all Invoice PDFs
- 60. Fetch list of customers with invoices from the database Transform fetched data to shape of PDF data Put completed PDF somewhere client can access Write the Invoice PDF for each customer Combine all Invoice PDFs do not need to fetch all invoice data Fetch invoice data for customers fetching 1/10 amount of data transforming 1/10 amount of data writing PDF for 1/10 customers worker dyno worker dyno