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The series so far:
In this post we’re going to go beyond the previous Hello World example and show you how to use the SWF extensions library to model workflows with multiple steps and allow data to flow naturally from one step to the next.
When using the extension library, the input to a workflow execution is passed onto the first activity of a workflow as input by default (as per the previous Hello World example), and the result of that activity is passed onto the next activity as input and so on. The result of the last activity is then used as the result of the whole workflow :
When you model an activity using the Activity type you need to pass in a function with the signature of string –> string. This function is called against the input when the generated activity worker receives a task, and will use the return value from the function as the result of the activity.
What you might not realize is that the Activity type is actually a specialized form of the generic Activity<TInput, TOutput> type which allows you to supply functions with arbitrary input and output types and simply uses the ServiceStack.Text JSON serializer to marshal data to and from string. I had decided to use the ServiceStack.Text serializer because it’s the fastest JSON serializer around based on my benchmarks.
Example : Sum Web Page Lengths
Suppose you want to count and sum the size of the HTML pages given a number of URLs and return the sum as the result:
To implement this workflow you need to attach two activities to the workflow, the first requiring a function that turns a string array into an int array and the second aggregates the int array into a single integer value, something along the lines of:
The main things to take away from this example is that:
- you can attach multiple activities to a workflow by chaining them up with the ++> operator
- handler functions for activities do not have to have string –> string signature
Let’s take a closer look at the two activities:
As you can see, given the input JSON string to the workflow:
[ “http://www.google.com”, “http://www.yahoo.com”, “http://www.bing.com” ]
the activities did what they were supposed to and first translated the input into an int array before summing them to give a total for the length of the landing pages for Google, Yahoo and Bing, and little surprise that Yahoo’s landing page is nearly an order of magnitude bigger than the rest!
In this post I demonstrated how to model a workflow with multiple steps which accept and return arbitrary types as input and output. In the next post I’ll demonstrate how to schedule multiple activities to be performed in parallel as a single step of a workflow.
Hi, I’m Yan. I’m an AWS Serverless Hero and I help companies go faster for less by adopting serverless technologies successfully.
Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.
Skill up your serverless game with this hands-on workshop.
My 4-week Production-Ready Serverless online workshop is back!
This course takes you through building a production-ready serverless web application from testing, deployment, security, all the way through to observability. The motivation for this course is to give you hands-on experience building something with serverless technologies while giving you a broader view of the challenges you will face as the architecture matures and expands.
We will start at the basics and give you a firm introduction to Lambda and all the relevant concepts and service features (including the latest announcements in 2020). And then gradually ramping up and cover a wide array of topics such as API security, testing strategies, CI/CD, secret management, and operational best practices for monitoring and troubleshooting.
If you enrol now you can also get 15% OFF with the promo code “yanprs15”.
Check out my new podcast Real-World Serverless where I talk with engineers who are building amazing things with serverless technologies and discuss the real-world use cases and challenges they face. If you’re interested in what people are actually doing with serverless and what it’s really like to be working with serverless day-to-day, then this is the podcast for you.
Check out my new course, Learn you some Lambda best practice for great good! In this course, you will learn best practices for working with AWS Lambda in terms of performance, cost, security, scalability, resilience and observability. We will also cover latest features from re:Invent 2019 such as Provisioned Concurrency and Lambda Destinations. Enrol now and start learning!
Check out my video course, Complete Guide to AWS Step Functions. In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. There is something for everyone from beginners to more advanced users looking for design patterns and best practices. Enrol now and start learning!
Here is a complete list of all my posts on serverless and AWS Lambda. In the meantime, here are a few of my most popular blog posts.
- All you need to know about caching for serverless applications
- Choreography vs Orchestration in the land of serverless
- Are Lambda-to-Lambda calls really so bad?
- Lambda optimization tip – enable HTTP keep-alive
- You are wrong about serverless and vendor lock-in
- You are thinking about serverless costs all wrong
- Check-list for going live with API Gateway and Lambda
- How to choose the right API Gateway auth method
- AWS Lambda – should you have few monolithic functions or many single-purposed functions?
- Guys, we’re doing pagination wrong
- Top 10 Serverless framework best practices
- I left full-time employment, here’s what happened since
- How to break the “senior engineer” career ceiling
- My advice to junior developers