Organizations building event-driven applications on Amazon EventBridge typically start with a single custom event bus in one account. This works well when a single team owns the architecture. As adoption grows across the organization, though, things get complicated. AWS best practices recommend a multi-account structure, which means each team runs in its own account. To route events between them, teams create multiple event buses connected through cross-account rules or bus-to-bus configurations. This workaround reintroduces the operational complexity that serverless architectures are meant to eliminate. Platform teams lose visibility into who is subscribing to which events, cross-account and bus-to-bus routing charges compound quickly, and teams that need capabilities like event ordering are forced to build complex workarounds or adopt entirely different technologies.

Today, we are announcing an enhanced custom event bus in Amazon EventBridge, purpose-built for organizations scaling event-driven applications across teams and accounts. With the new enhanced custom event bus, you can deploy a single, centralized event bus shared across all AWS accounts in your organization, with ordering guarantees, a simplified Subscriber resource, and a new pricing model that delivers improved economics at scale and cost allocation for publishers and subscribers.

Let’s try it out
To get started with an enhanced custom event bus, I navigated to the EventBridge console in the AWS Management Console and opened the Create custom event bus page. I selected Custom event bus, the recommended option labeled New. The page also offered Custom event bus – classic, which continues to receive events and route them with rules and targets. Below the selection, EventBridge showed how the new bus works. One shared bus serves every team in the organization. Publishers send events, subscribers consume only what they need, and EventBridge handles ordering, retention, routing, and delivery.

The Create custom event bus page. Custom event bus is the recommended new option, with ordered delivery, filter patterns, event replay, and sharing across your AWS organization. Custom event bus – classic remains available for existing workloads.

Next, I configured resource sharing. I turned on Enable event bus sharing and selected Allow sharing only within your organization. I chose AWS account ID as the principal type. I could also share with an organization, an organizational unit, or an AWS Identity and Access Management (IAM) role or user. Sharing uses AWS Resource Access Manager (AWS RAM), so I did not have to set up cross-account permissions or bus-to-bus routing myself.

Resource sharing on the new custom event bus. I enabled sharing within my organization through AWS RAM and selected an AWS account as the principal, which is how teams publish and subscribe on the same bus without extra routing.

Organization-wide sharing
With the new enhanced custom event bus, you can create a single event bus and share it across all AWS accounts in your organization. Platform teams deploy one bus and establish it as the central event backbone, eliminating the need to configure cross-account permissions or bus-to-bus routing. Application teams across your organization can publish and subscribe to events on the same bus without waiting for infrastructure provisioning.

Publishers send events without needing to know which teams consume them, and subscribers create their own Subscriptions independently. Platform teams maintain visibility into all event flows and fine-grained control over who can publish and consume events. The new enhanced custom event bus has a default quota of 10,000 Subscribers per bus, and you can request a higher quota. That reduces the fragmentation that occurs when subscriber limits force you to split across multiple buses.

Event ordering
Event-driven architectures work best when consumers are designed around asynchronous patterns, where the order of events does not matter. There are a few cases where order does matter. In a logistics application, driver location updates must arrive in sequence. Out-of-sequence events cause routing algorithms to make decisions based on stale data.

The enhanced custom event bus supports both patterns on the same bus. Publishers can include an EventGroupId when sending events. EventBridge delivers events that share the same EventGroupId in sequence to Subscribers that chose ordered delivery. Other subscribers on that bus can receive the same events without ordering. You can keep events for each driver in the correct order without building complex workarounds, while the rest of your consumers stay fully asynchronous.

To support ordered processing, the enhanced custom event bus includes synchronous invocation for targets like AWS Lambda. Synchronous mode confirms successful processing before acknowledging the event, eliminating the common pattern of placing Amazon Simple Queue Service (Amazon SQS) between an event bus and Lambda to ensure reliability.

Subscriptions
The enhanced custom event bus introduces the Subscriber resource, which combines event filtering, target configuration, retry policies, and dead-letter destinations into a single, manageable unit. Today, achieving the same outcome with EventBridge requires configuring separate rules, targets, and retry settings across multiple resources. Subscribers simplify this by giving each consumer one resource that defines what events they want, where to deliver them, and how to handle failures.

Subscribers also include variable start time options, making it easier for teams to onboard new consumers or replay events to recover from application errors or hydrate new applications.

Event evaluation
Publishers can turn on content-based deduplication so EventBridge detects and drops retries of the same event from the payload itself. You do not have to generate and track a deduplication ID when a timeout or a partial failure sends the same event twice. EventBridge hashes the meaningful parts of the event and collapses matches that arrive within five minutes, which gives those retries exactly-once delivery semantics instead of EventBridge’s usual at-least-once model. If you already stamp your own idempotency token, keep using it. Content-based deduplication is for sources that cannot reliably identify the same event on a retry.

Subscribers can use JSONata expressions to reshape an event before it reaches a target, extracting fields, renaming them, or computing new values when a downstream API expects a different shape. If you already produce Apache Avro or Protocol Buffers events, EventBridge can deserialize those payloads to JSON, allowing subscribers fine grained filtering and routing on the full event payload without having to consume, deserialize, and match or discard on their own.

New pricing model
The enhanced custom event bus uses a new ingress and egress throughput pricing model. Publishers pay for events ingested, and subscribers pay for events delivered. This replaces the per-event model where cross-account and bus-to-bus routing charges compound in multi-bus architectures. For pricing details, visit the EventBridge pricing page.

Existing EventBridge custom event buses continue to work as they do today with no changes required. They now appear as Custom event bus – classic. The enhanced custom event bus is a new resource that you adopt at your own pace. In the console, it appears as Custom event bus.

Now available
The enhanced custom event bus is available today in the US East (N. Virginia, Ohio), US West (Oregon), Europe (Ireland, Frankfurt, Stockholm, Spain), and Asia Pacific (Hong Kong, Malaysia, Mumbai, Singapore, Sydney, Thailand, Tokyo) Regions. You can create your first enhanced custom event bus through the AWS Management Console, AWS Command Line Interface (AWS CLI), or EventBridge APIs. To get started, visit the EventBridge documentation or try it out directly in the EventBridge console.

Today, we are announcing AWS Lambda MicroVMs, a new serverless compute primitive within AWS Lambda that lets you run code generated by users or AI in isolated, stateful execution environments. You get virtual machine level isolation, near-instant launch and resume, and direct control over environment lifecycle and state, all without managing infrastructure or building expertise in complex virtualization technologies. Lambda MicroVMs are powered by Firecracker, the same lightweight virtualization technology that has powered over 15 trillions of monthly Lambda function invocations.

Why customers need this
Over the past few years a new class of multi-tenant applications has emerged that all share the need to hand each end user their own dedicated execution environment in which to safely run code that the application developer did not write. AI coding assistants, interactive code environments, data analytics platforms, vulnerability scanners, and game servers that run user-supplied scripts all fit this pattern. Building that capability today means making a difficult choice. Virtual machines deliver strong isolation but take minutes to start. Containers launch in seconds, yet their shared-kernel architecture requires significant custom hardening to safely contain untrusted code. Functions as a service are optimized for event-driven, request-response workloads, but are not designed for long-running interactive sessions that need to retain environment state across user interactions. That leaves developers either accepting tradeoffs between performance and isolation, or investing significant engineering resources to build and operate custom virtualization infrastructure to achieve isolated execution while delivering low-latency experiences to end-users. This presents an effort that demands deep expertise and pulls engineering time away from the product they are actually trying to build.

Lambda MicroVMs is purpose-built for exactly this gap. Each MicroVM gives a single end user or session its own isolated environment that launches rapidly, retains memory and disk state for the length of the session, and pauses to a low idle cost when the user steps away. Because the same Firecracker technology already underpins AWS Lambda Functions, you inherit the operational maturity of a service that has been running this stack at scale.

Let’s try it out
To get started, I navigated to the AWS Lambda console, where Lambda MicroVMs now appears in the left-hand navigation menu. I first need to create a MicroVM Image.

I packaged a Flask web app and its Dockerfile into a zip file, uploaded it to an Amazon Simple Storage Service (Amazon S3) bucket.

My Flask API – app.py

import logging

from flask import Flask, jsonify

app = Flask(__name__)
logging.basicConfig(level=logging.INFO)


@app.route("/")
def hello():
    app.logger.info("Received request to hello world endpoint")
    return jsonify(message="Hello, World!")


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

My Dockerfile

FROM public.ecr.aws/lambda/microvms:al2023-minimal
RUN dnf install -y python3 python3-pip && dnf clean all

WORKDIR /app

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY app.py .

EXPOSE 5000

CMD ["gunicorn", "--bind", "0.0.0.0:5000", "app:app"]

I used the following command to create my MicroVM Image.

aws lambda-microvms create-microvm-image \
--code-artifact uri=<path/to/s3/artifact.zip> --name <VM_image_name> \
--base-image-arn arn:aws:lambda:us-east-1:aws:microvm-image:al2023-1 \
--build-role-arn <IAM role ARN>

You can also create the MicroVM Image in the AWS Console as in the image above. Once I ran the command, Lambda retrieved the zip, ran the Dockerfile, initialized the application, and took a Firecracker snapshot of the running disk and memory state. Build logs streamed in real time to Amazon CloudWatch under /aws/lambda/microvms/<image-name>, and when the image was ready it appeared in the console with its Amazon Resource Name (ARN) and version number.

aws lambda-microvms run-microvm \
--image-identifier arn:aws:lambda:<region>:<acct>:microvm-image:my-image \
--execution-role-arn arn:aws:iam::<acct>:role/MicroVMExecutionRole \
--idle-policy '{"maxIdleDurationSeconds":900,"suspendedDurationSeconds":300,"autoResumeEnabled":true}'

Launching can also be done via the AWS Console or the CLI. I passed the image ARN and an idle policy configured to auto-suspend after 15 minutes of inactivity and auto-resume on the next incoming request. No networking setup was required. Lambda assigned the MicroVM a unique ID, returned a dedicated endpoint URL, and started a new MicroVM with my Flask app already running, since it was resumed from a snapshot. My Flask app was already running the moment the launch completed. One API call to get a fully initialized, bootstrapped compute environment.

To send traffic, I generated a short-lived auth token with the CLI and attached it to a plain HTTPS request using the X-aws-proxy-auth header. The request landed on my Flask app immediately. I then let the MicroVM sit idle past the suspend threshold, at which point the MicroVM was suspended, with its memory and disk state snapshotted and stored. I then sent another request, and it resumed with the application state fully intact. From the client side, the pause never happened.

How it works
Under the covers, Lambda MicroVMs delivers three capabilities that, until today, no single AWS compute service offered together. The first is virtual machine level isolation, which comes from Firecracker. Each session runs in its own dedicated MicroVM with no shared kernel and no shared resources between users, so untrusted code supplied by one user is contained to their execution environment, without access to other environments or the underlying system. The second is rapid launch and resume. The model is image-then-launch: you create a MicroVM Image by supplying a Dockerfile and code packaged as a zip artifact in Amazon S3, and Lambda runs your Dockerfile, initializes your application, and takes a Firecracker snapshot of the running environment’s memory and disk state. Every subsequent MicroVM launched from that image resumes from the pre-initialized snapshot rather than booting cold, which means launches and idle resumes both achieve near-instant startup latency. Even a multi-gigabyte interactive session comes back online quickly enough to feel responsive to the end user. The third is stateful execution. A running MicroVM retains memory, disk, and running processes across the user’s session. During idle periods, a MicroVM can be suspended – with memory and disk state intact – and resumed when traffic arrives. Installed packages, loaded models, and working filesets are readily available when the user resumes their session. MicroVMs support up to 8 hours of total runtime and can be suspended automatically after a configurable idle window, which makes it straightforward to build products as varied as software vulnerability scans that complete in minutes, data analytics applications that run for hours, and interactive coding sessions with extended idle periods. As Lambda MicroVMs are started from pre-initialized snapshots, applications generating unique content, establishing network connections, or loading ephemeral data during initialization may need to integrate with service-provided hooks for compatibility.

Lambda MicroVMs is a new resource within AWS Lambda, with a distinct API surface. Lambda Functions remain the right choice for event-driven, request-response workloads, and Lambda MicroVMs is purpose-built for multi-tenant applications that need to hand each end user or session their own isolated environment to execute user- or AI-generated code. The two complement each other. An application using Lambda Functions for its event-driven backbone can call into Lambda MicroVMs for the steps that need to run untrusted code in isolation. You bring the application, and the service delivers the execution environment.

Now available
AWS Lambda MicroVMs is available today in the US East (N. Virginia, Ohio), US West (Oregon), Europe (Ireland) and Asia Pacific (Tokyo) Regions, on the ARM64 architecture, with up to 16 vCPUs, 32 GB of memory, and 32 GB of disk per MicroVM. Idle MicroVMs can be suspended explicitly through an API call or automatically through a lifecycle policy, which reduces the running cost while preserving full state for fast resume. Pricing details can be found on the AWS Lambda pricing page.

To get started, visit the AWS Lambda console, or learn more on the Lambda MicroVMs product page. For documentation, see the Lambda MicroVMs Developer Guide.