Lambda vs. Fission on EKS: Simplified Cost Breakdown and Real-World Use Cases

In this post, we’re diving into the real differences between AWS Lambda and Fission on EKS, but let’s keep it simple and straightforward—because it’s not just about the raw numbers. It’s about how much time and effort you need to put in as well.

We’re assuming you already have an EKS cluster (because setting up a cluster just to run Fission functions wouldn’t make sense). Plus, we’ll give you an additional example for spot instances (read more about spot instances in EKS)—because let’s be honest, those savings can’t be ignored.

AWS Lambda: Simple, Quick, and Easy to Use

AWS Lambda is the go-to solution for serverless computing if you want to run your functions without thinking too much about the infrastructure. No managing servers, no dealing with clusters, just pay for what you use.

But what’s the real cost behind Lambda? And when does it make sense to use?

Lambda Cost Breakdown (without the headache):

Lambda charges you for:

1. How often your function runs (number of requests).
2. How long it runs for (compute time).

Here’s a simple example:

• For 1 million requests per month, with a function using 128MB memory, you’re looking at about $0.62/month.
• Bump that up to 10 million requests, and it’s around $6.20/month.

If your workload is sporadic—like an API that gets hit a few times throughout the day—Lambda’s pay-per-use model works out to be extremely affordable. Plus, you don’t need to think about managing or scaling anything yourself, which cuts down on maintenance and personnel costs big time.

Maintenance and Personnel Costs for Lambda: Nearly zero. AWS takes care of everything under the hood. Your team only needs to write and manage the code—no infrastructure babysitting required. So, no dedicated personnel needed for infrastructure management = more savings on staff costs.

Spot Instance: Not Happening in Lambda

There’s no spot instance version of Lambda, because AWS takes full control of managing the infrastructure for you. If you want to dive into using spot instances to cut costs, that’s where Fission on EKS comes into play.

Fission on EKS: Flexibility and Control (with a Side of Responsibility)

Fission on EKS is all about flexibility—it’s designed to let you run serverless functions but within your own Kubernetes setup. That gives you a lot more control, but here’s the catch: you’re managing the infrastructure. Yes, you can scale, tune, and optimize, but it takes more hands-on work. So, keep in mind that personnel costs come into play here.

Fission on EKS Cost Breakdown (Nice and Simple):

If you’re running Fission on EKS, your cost comes from the compute resources in your EKS cluster. For simplicity, let’s say you have an m5.large EC2 instance (2 vCPUs, 8GB RAM) running your Kubernetes pods:

• An on-demand m5.large costs around $0.096/hour.
• If your function uses 25% of that instance’s capacity, you’d pay $0.024/hour for it.
• Over a month, that’s about $17.52 for one continuously running function.

Spot Instance Example: Fission on EKS

Now, let’s talk spot instances. These can save you up to 70-90% on your EC2 costs. So, for the same m5.large instance using spot pricing, you might pay $0.03/hour instead:

• 25% of a spot instance would be $0.0075/hour.
• Over a month, that’s just $5.48/month.

With Fission on spot instances, your compute costs drop dramatically. However, you need to be aware of spot instance interruptions—so, this option makes sense for non-critical workloads that can handle being paused or restarted.

Maintenance and Personnel Costs for Fission on EKS: Medium. Running Fission means someone on your team needs to be comfortable managing Kubernetes. That means either dedicated DevOps personnel or someone willing to juggle that role. This comes with time costs and potential mistakes, which can add up.

When to Use AWS Lambda: The Convenience Factor

Lambda isn’t just a low-maintenance tool—it’s designed to let you focus on the code, not the infrastructure. So when does it make sense to use Lambda?

Lambda is Great When:

• Your traffic is unpredictable: Lambda shines when you don’t know when your app will get hit. You pay only for the time your function is active, so for bursty workloads, it’s ideal.
• You don’t want to manage infrastructure: Lambda takes the management work off your plate entirely, reducing your team’s operational burden.
• You want cost clarity: You know exactly what you’re paying for each month. No surprises.

Example: If you run a website that only gets hit a few times a day (like a couple thousand requests), Lambda is perfect. 5,000 requests/day would cost you around $93/year. It’s simple, easy to scale, and stress-free.

When to Use Fission on EKS: Flexibility at Scale

Fission works best when you’ve already invested in an EKS cluster and need full control over how your functions are deployed. Plus, you can run multiple functions across the same instance, optimizing your resources and potentially lowering your overall costs.

Fission on EKS is Great When:

• You already run Kubernetes: If your team is comfortable with Kubernetes, Fission lets you extend your serverless capabilities without adding tons of overhead.
• You’re dealing with high traffic: For continuous, high-volume workloads, Fission’s flexibility (especially with spot instances) lets you scale while keeping costs down.
• You want to use spot instances: For non-critical functions, spot instances save you significant compute costs.

Example: A data pipeline that processes 30 million events/month. Running that in Lambda might cost around $186/month. But running it in Fission on spot instances could drop the cost to around $30/month. The downside? Someone needs to manage the Kubernetes infrastructure.

Considering Maintenance and Personnel Costs

One big consideration that often gets glossed over is the cost of maintaining your infrastructure. This is where Lambda really shines compared to Fission.

Lambda Maintenance Costs:

With Lambda, there’s no infrastructure to maintain. That means:

• No need for a dedicated DevOps team to manage Kubernetes clusters.
• Less time spent optimizing resources, scaling, or troubleshooting infrastructure issues.

So, even if Lambda is more expensive per function, the time and personnel savings can make up for that. Plus, for startups or small teams, Lambda’s simplicity means fewer overhead costs for managing the service.

Fission on EKS Maintenance Costs:

Running Fission in EKS means you’re responsible for:

• Managing the Kubernetes cluster (scaling, monitoring, and resource optimization).
• Handling interruptions if you’re using spot instances, which requires smart architecture to ensure your services can handle potential downtime.
• Personnel costs: You’ll likely need a DevOps engineer or someone with Kubernetes expertise on the team, which can add to your overall expenses.

If your team is already running EKS for other services, adding Fission might not be a big lift. But if you’re a smaller team without deep Kubernetes expertise, those maintenance costs can become a burden.

Lambda vs. Fission on EKS: Simplified Decision Guide

When to Use Lambda:

• Low to medium traffic: Great for bursty workloads where you don’t want to pay for idle time.
• No infrastructure overhead: Perfect for teams that want to focus on development and not infrastructure management.
• Clarity in costs: You know exactly what you’ll pay each month, and it’s simple to calculate.

When to Use Fission on EKS:

• You’ve got EKS expertise: If you already know your way around Kubernetes, Fission on EKS is a great way to leverage your existing infrastructure.
• High traffic, continuous workloads: Especially if you want to use spot instances to cut costs on long-running, non-critical functions.
• Flexibility is key: If you need granular control over scaling and resource allocation, Fission on EKS gives you that flexibility.

Final Thoughts: The Right Tool for the Job

At the end of the day, the decision between Lambda and Fission comes down to your specific needs. If you’re looking for simplicity and zero management overhead, Lambda is your best bet. But if you’re ready to take control of your infrastructure and want to optimize costs using spot instances, Fission on EKS is a powerful tool in your arsenal.

And remember: it’s not just about the raw compute cost. Consider the personnel and maintenance overhead too. Sometimes, the simpler option might save you more in the long run by freeing up your team’s time and energy.