Yubl’s road to Serverless — Part 1, Overview

The Road So Far

part 2 : testing and continuous delivery strategies

part 3 : ops

part 4 : building a scalable push notifications system

part 5 : building a better recommendation system

Since Yubl’s closure quite a few people have asked about the serverless architecture we ended up with and some of the things we have learnt along the way.

As such, this is the first of a series of posts where I’d share some of the lessons we learnt. However, bear in mind the pace of change in this particular space so some of the challenges/problems we encountered might have been solved by the time you read this.

ps. many aspects of this series is already covered in a talk I gave on Amazon Lambda at Leetspeak in 2016, you can find the slides and recording of the talk here.

From A Monolithic Beginning

Back when I joined Yubl in April I inherited a monolithic Node.js backend running on EC2 instances, with MongoLab (hosted MongoDB) and CloudAMQP (hosted RabbitMQ) thrown into the mix.

There were numerous problems with this legacy system, some could be rectified with incremental changes (eg. blue-green deployment) but others required a rethink at an architectural level. Although things look really simple on paper (at the architecture diagram level), all the complexities are hidden inside each of these 3 services and boy, there were complexities!

My first tasks were to work with the ops team to improve the existing deployment pipeline and to draw up a list of characteristics we’d want from our architecture:

able to do small, incremental deployments
deployments should be fast, and requires no downtime
no lock-step deployments
features can be deployed independently
features are loosely coupled through messages
minimise cost for unused resources
minimise ops effort

From here we decided on a service-oriented architecture, and Amazon Lambda seemed the perfect tool for the job given the workloads we had:

lots of APIs, all HTTPS, no ultra-low latency requirement
lots of background tasks, many of which has soft-realtime requirement (eg. distributing post to follower’s timeline)

To a Serverless End

It’s suffice to say that we knew the migration was going to be a long road with many challenges along the way, and we wanted to do it incrementally and gradually increase the speed of delivery as we go.

“The lead time to someone saying thank you is the only reputation metric that matters”

– Dan North

The first step of the migration was to make the legacy systems publish state changes in the system (eg. user joined, user A followed user B, etc.) so that we can start building new features on top of the legacy systems.

To do this, we updated the legacy systems to publish events to Kinesis streams.

Our general strategy is:

build new features on top of these events, which usually have their own data stores (eg. DynamoDB, CloudSearch, S3, BigQuery, etc.) together with background processing pipelines and APIs
extract existing features/concepts from the legacy system into services that will run side-by-side
these new services will initially be backed by the same shared MongoLab database
other services (including the legacy ones) are updated to use hand-crafted API clients to access the encapsulated resources via the new APIs rather than hitting the shared MongoLab database directly
once all access to these resources are done via the new APIs, data migration (usually to DynamoDB tables) will commence behind the scenes
wherever possible, requests to existing API endpoints are forwarded to the new APIs so that we don’t have to wait for the iOS and Android apps to be updated (which can take weeks) and can start reaping the benefits earlier

After 6 months of hard work, my team of 6 backend engineers (including myself) have drastically transformed our backend infrastructure. Amazon was very impressed by the work we were doing with Lambda and in the process of writing up a case study of our work when Yubl was shut down at the whim of our major shareholder.

Here’s an almost complete picture of the architecture we ended up with (some details are omitted for brevity and clarity).

Some interesting stats:

170 Lambda functions running in production
roughly 1GB of total deployment package size (after Janitor Lambda cleans up unreferenced versions)
Lambda cost was around 5% of what we pay for EC2 for a comparable amount of compute
the no. of production deployments increased from 9/month in April to 155 in September

For the rest of the series I’ll drill down into specific features, how we utilised various AWS services, and how we tackled the challenges of:

centralised logging
centralised configuration management
distributed tracing with correlation IDs for Lambda functions
keeping Lambda functions warm to avoid coldstart penalty
auto-scaling AWS resources that do not scale dynamically
automatically clean up old Lambda function versions
securing sensitive data (eg. mongodb connection string, service credentials, etc.)

Links

Like what you’re reading but want more help? I’m happy to offer my services as an independent consultant and help you with your serverless project — architecture reviews, code reviews, building proof-of-concepts, or offer advice on leading practices and tools.

I’m based in London, UK and currently the only UK-based AWS Serverless Hero. I have nearly 10 years of experience with running production workloads in AWS at scale. I operate predominantly in the UK but I’m open to travelling for engagements that are longer than a week. To see how we might be able to work together, tell me more about the problems you are trying to solve here.

I can also run an in-house workshops to help you get production-ready with your serverless architecture. You can find out more about the two-day workshop here, which takes you from the basics of AWS Lambda all the way through to common operational patterns for log aggregation, distribution tracing and security best practices.

If you prefer to study at your own pace, then you can also find all the same content of the workshop as a video course I have produced for Manning. We will cover topics including:

authentication & authorization with API Gateway & Cognito
testing & running functions locally
CI/CD
log aggregation
monitoring best practices
distributed tracing with X-Ray
tracking correlation IDs
performance & cost optimization
error handling
config management
canary deployment
VPC
security
leading practices for Lambda, Kinesis, and API Gateway

You can also get 40% off the face price with the code ytcui. Hurry though, this discount is only available while we’re in Manning’s Early Access Program (MEAP).