Lambda in 2026: Durable Functions and Managed Instances Explained
Two new capabilities that expand what you can do with AWS Lambda: long-running stateful workflows and functions running on managed EC2 instances. What they are, how they differ, and when each one makes sense.
Lambda is AWS’s serverless compute service: you upload code and AWS runs it when an event happens. It has two well-known limitations. First, each invocation can last at most 15 minutes. Second, it is often criticized for cost under heavy, steady load, since a common complaint is that pay-per-use Lambda gets expensive at scale. theburningmonk
At re:Invent 2025, AWS addressed both with two new capabilities.
1. Lambda Durable Functions
Announced on December 2, 2025, they let you build multi-step applications and AI workflows inside Lambda. They checkpoint progress automatically, can suspend execution for up to a year, and recover from failures without you managing extra infrastructure. amazon
How they work:
- They add new operations called “steps” (checkpointed units of work) and “waits” (pauses), and you are not charged for compute while an execution is paused. amazon
- They are expressed as code, unlike Step Functions, which uses YAML definitions. They rely on a replay mechanism: AWS may run your function several times for the same request, restoring the state from earlier passes. infoq infoq
- On top of the usual per-invocation timeout, there is an execution timeout for the total duration, which can span several invocations. They support dead-letter queues (DLQs) but not Lambda destinations. theburningmonk
Languages: at launch, Python 3.13/3.14 and Node.js 22/24, initially in US East (Ohio). More followed: a Java SDK in developer preview (February 2026) and a .NET SDK that became generally available in July 2026, aimed at cases such as payment pipelines, AI agent orchestration, and human-in-the-loop approvals. AWS Lambda announces durable functions for multi-step applications and AI workflows
2. Lambda Managed Instances
This lets you run Lambda functions on EC2 instances in your account, while AWS manages the instance lifecycle, OS and runtime patching, routing, load balancing, and auto scaling. amazon
- Who it is for: workloads that need specialized hardware, or that are steady and predictable. You can use EC2 pricing models such as Savings Plans and Reserved Instances, and access processors like Graviton4. amazon
- Pricing: the EC2 instance cost plus a 15% management fee and $0.20 per million requests, with no duration charge. Each instance handles several concurrent requests and has a maximum lifetime of 14 days. devclass devclass
- Trade-offs: for light usage it is not a good fit, because the instances exist even when no functions are running. Also, GPU instances are not supported. devclass theburningmonk
- Availability: in June 2026 it expanded to nearly all commercial AWS Regions. amazon
3. Quick comparison
| Classic Lambda | Durable Functions | Managed Instances | |
|---|---|---|---|
| Solves | Short, event-driven tasks | Long workflows with state | Steady loads or specific hardware |
| Example | Light API, file processing | Payments, approvals, AI workflows | Stable high-volume traffic |
| Watch out for | 15-minute limit | Replayable (re-executed) logic | You pay for capacity even when idle |
4. My take
I have used Lambda only in a limited way, mostly for integrations with S3 and DynamoDB and for event-driven tasks, so I can’t claim deep production experience with these new features. Still, they change how I think about my backend. In my own architecture, I keep Postgres and RabbitMQ on EC2 with EFS, because they are always-on, stateful services that don’t fit Lambda’s event-driven model. Durable Functions look interesting for multi-step flows with waiting periods, such as payment confirmations or approvals, which I would have handled with extra services before. Managed Instances seem more relevant if my API traffic ever becomes steady and predictable. I haven’t tested either yet, so I see this article as a starting point for what I want to try next.
One point worth noting: Durable Functions look a lot like Step Functions, and there is still debate about when to pick each. One industry commentator said that before this announcement he would typically recommend Step Functions, so there is no single rule. infoq
5. Getting started
- Durable Functions: the developer guide and the official announcement.
- Managed Instances: the launch blog and the documentation.
- Always check current pricing and Regions before deciding, since they can change.
References
- Durable Functions announcement: https://aws.amazon.com/about-aws/whats-new/2025/12/lambda-durable-multi-step-applications-ai-workflows/
- Durable Functions developer guide: https://docs.aws.amazon.com/lambda/latest/dg/durable-functions.html
- InfoQ coverage: https://infoq.com/news/2025/12/aws-lambda-durable-functions/
- Java SDK (developer preview): https://aws.amazon.com/about-aws/whats-new/2026/02/lambda-durable-execution-java-preview
- .NET SDK (generally available): https://aws.amazon.com/about-aws/whats-new/2026/07/lambdadf-dotnet/
- Managed Instances announcement: https://aws.amazon.com/about-aws/whats-new/2025/11/aws-lambda-managed-instances/
- Launch blog post: https://aws.amazon.com/blogs/aws/introducing-aws-lambda-managed-instances-serverless-simplicity-with-ec2-flexibility
- Pricing analysis (DevClass): https://www.devclass.com/serverless/2025/12/01/aws-debuts-lambda-managed-instances-on-ec2-more-control-lower-cost-for-high-volume-users/1726760
- re:Invent 2025 serverless roundup: https://theburningmonk.com/2025/12/the-biggest-reinvent-2025-serverless-announcements/
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