Amazon EKS runs hundreds of thousands of Kubernetes clusters across more than thirty AWS regions. Operating at that scale has taught us something that has shaped how we build the service and that we think is useful to anyone running Kubernetes at scale: most availability problems do not stem from a component failing. They come from a component reacting to a problem in a way that makes it worse. A cache that goes stale and serves wrong answers. A health check that restarts the very process keeping a cluster alive.

What separates a resilient control plane from a fragile one is not the number of faults. It is whether a fault stays a fault or becomes an outage. This post is the story of how we keep the EKS-managed Kubernetes control plane on the right side of that line at ever-growing scale: the foundational changes we made and why, and what operating at fleet scale taught us about building systems that tolerate faults rather than spreading them. These are the reasons our most demanding customers confidently run their mission-critical workloads on EKS.

How AI and analytics workloads reshaped what “scale” means

Kubernetes was built for a particular rhythm of work. Pods came and went at predictable rates, and controllers had seconds or minutes to reconcile. The system’s design reflected that pace: strong data consistency, ordered watches, and consensus-replicated storage that puts correctness first. It worked beautifully for what it was designed to do, and it still does.

“What separates a resilient control plane from a fragile one is not the number of faults. It is whether a fault stays a fault or becomes an outage.”

But the workloads evolved faster than anyone anticipated. Foundation model training runs scale-up training jobs on thousands of GPU nodes in minutes. Real-time inference services scale from a warm baseline to thousands of replicas, then drop back within the hour. Apache Spark analytics pipelines burst from zero to tens of thousands of executor pods, chew through a dataset, and vanish. 

Emerging agentic AI workloads add yet another dimension: autonomous agents that spin up, fan out, execute tasks, and tear down in seconds or less. These workloads share a trait that distinguishes them from traditional microservices: they generate enormous volumes of state transitions within compressed time windows and are deeply intolerant of delays. This velocity of state change pushed us to reinvent some of the mechanics to support a scale that was previously impossible, and to contribute what we could upstream.

How EKS reimagined Kubernetes storage foundation

Every Kubernetes cluster depends on etcd as its source of truth. Every application, every service endpoint, every scheduling decision is stored there. If etcd loses data, the cluster forgets everything it knows. Protecting that state is the most important job for a managed Kubernetes service.

Operating etcd for one cluster is well understood. Operating it for a fleet of millions is a different problem entirely. Hardware fails, networks blip, and disks degrade, so something has to handle those events without a human in the loop. And the operations etcd needs most, like replacing a failed member or recovering after a zonal event, are exactly the ones where a person acting under pressure can make a mistake that causes permanent data loss.

From the beginning, we built an operator agent that runs alongside every etcd instance and automates its entire lifecycle. The agent has two jobs. First, backup and recovery: it takes point-in-time snapshots and stores them durably outside the cluster. If too many instances are lost at once and the survivors cannot form a majority, the agent automatically detects the condition and rebuilds from the latest snapshot. Second, membership management: when an instance fails, the agent removes the terminated member and adds its replacement in an order that protects quorum and prevents split-brain.

A recent, more fundamental change was replacing etcd’s consensus mechanism, Raft, with a purpose-built journal that provides durable, ordered storage independently of etcd. In traditional etcd, a majority of members must agree on every write before it is committed. If two of three are unhealthy, the cluster becomes unavailable. 

By offloading durability to the journal, etcd peers no longer negotiate quorum among themselves. Writes commit as soon as the journal acknowledges persistence, and that entire class of etcd quorum-loss failures disappeared. Since the journal handles persistence, etcd no longer needs to fsync writes to local disk, so its data store has moved to an in-memory filesystem. What was a disk-bound system became a compute-bound one, and storage latency was removed entirely from the critical path. For a deeper look at this architecture, read “Under the hood: Amazon EKS ultra scale clusters.”

“What was a disk-bound system became a compute-bound one, and storage latency was removed entirely from the critical path.”

For ultra-scale clusters, we went further and partitioned etcd into resource-specific shards. Each partition operates independently with its own storage budget and throughput capacity. The primary value is failure isolation. In a monolithic deployment, if the events keyspace exceeds its quota because a misbehaving controller creates objects faster than garbage collection can remove them, it blocks writes to everything, including node leases. 

Suddenly, healthy nodes appear unhealthy because their lease renewals are being rejected. With partitioned etcd, the events partition hits its quota, but the leases partition continues operating normally. Nodes remain healthy. The scheduler keeps running.

What replacing etcd’s consensus mechanism unlocked

Removing the quorum requirement allowed us to make a change we had wanted for a long time: running etcd on the same host as the API server. In the traditional layout, every read and write crosses the network between separate machines. Each trip is fast on its own, but at thousands per second, the travel time adds up. With collocation, the API server talks to its local etcd over a loopback interface, and pod scheduling and controller reconciliation get measurably faster. For workloads where job controller queue depth is the binding constraint, shaving milliseconds off each API call means many more jobs are processed per second before the queue starts growing.

This is where the operator agent paid off. When etcd runs on the same host, an etcd member comes and goes whenever a control-plane host is replaced, which happens routinely. That only works if membership management is completely safe and automatic, which is exactly what the agent was already doing. We did not have to build a colocation from scratch; we built it on top of infrastructure that had been managing etcd membership safely since day one.

Collocation also taught us a lesson worth passing on: the convenient path needs a failover in case it breaks. The local etcd is the fast path, but if it becomes impaired, the API server fails over to another etcd member that is actively serving other API servers from the same journal. When you optimize for the common case, design just as deliberately for the moment that optimization is not available.

Fixing bottlenecks across the stack

At extreme scale, you have to address bottlenecks across the entire Kubernetes stack, and most of them are not bugs in the traditional sense. They are design choices that were correct at the scale Kubernetes originally targeted and break down only when the numbers get large. Rather than working around them internally, we fix them upstream so the entire community benefits.

One example involved the watch cache, the in-memory layer that distributes state changes from etcd to every controller watching for updates. When a controller starts, it requests a full snapshot of the current state via a mechanism called WatchList, and the existing implementation holds a shared read lock for the duration of the response build. 

At hundreds of thousands of objects, that work runs long enough to starve the writer that needs exclusive access, so the cache’s resource version cannot advance. Consistent reads see a stale cache and fail over to etcd, while the response building churns through hundreds of thousands of allocations under the lock. We identified this as a limitation in the watch-cache’s locking model and are working with the community to refactor the underlying data structures and interfaces to eliminate the contention.

The same shape appears elsewhere. In the Horizontal Pod Autoscaler, a single mutex protecting the scaling state becomes a serialization point at high HPA counts, where workers spend nearly all their time blocked rather than doing useful work. A redesigned data store (PR #139142) restores parallelism and raises reconciliation throughput by orders of magnitude. In the scheduler, we identified a bottleneck (issue #138426): every scheduling cycle rebuilds a set of in-use persistent volumes by scanning every node in the cluster, even for pods that do not use storage at all. The fix computes that information lazily, and only for pods that actually need it, restoring throughput at scale.

Each of these started from a real production workload hitting a cliff, and we are working on the fixes upstream so the improvements reach every Kubernetes user.

From engineering to guarantees: EKS Provisioned Control Plane

The engineering described above made the EKS control plane more resilient and performant. But customers had a different problem: they could observe that the control plane kept up today, but they could not reserve its capacity the way they reserve compute or GPU capacity. 

A team planning a thousand-node training run could secure the instances weeks in advance, yet had no equivalent mechanism for the orchestration layer that would coordinate them. EKS Provisioned Control Plane fills that gap. It exposes the control plane’s performance as dimensions you size explicitly, backed by the same kind of commitment you expect from the rest of your infrastructure.

You choose a scaling tier that maps to concrete, measurable capabilities: API request concurrency, pod scheduling rate, and cluster database size. The tiers range from XL through 8XL. At the top end, 8XL on Kubernetes 1.34 provides 16,000 concurrent API request seats, 400 pods-per-second scheduling rate, and 16 GB of cluster database storage, all backed by a 99.99% availability SLA measured in one-minute intervals.

Tiers are not static. You step up before a GPU training run or a large sales event, step back down during quiet periods, or grow permanently as your platform matures. Configuration happens through the console, CLI, eksctl, CloudFormation, or Terraform on any cluster, without recreation or downtime. 

For AI workloads, orchestration capacity is planned alongside GPU capacity, available when the compute comes online. For analytics platforms submitting hundreds of jobs per minute, the control plane is ready for the burst before it arrives. And for organizations that need environmental consistency across staging, production, and disaster recovery, the same tier guarantees consistent performance characteristics everywhere.


Taking the same foundation to the edge

Some workloads cannot move to the cloud, whether due to data sovereignty requirements, latency constraints, or unreliable connectivity to the Region. Running Kubernetes in these disconnected environments introduces unique challenges: etcd must remain durable on hardware with only a few machines, the cluster must self-heal without reaching the cloud, and observability must survive network partitions that last days. 

With the updated architecture for EKS local clusters on instance store Outposts, we brought edge clusters onto the same management plane and software stack as EKS clusters in the cloud.

The control plane lives in an EKS-managed account on the Outpost rather than in the customer’s account, so customers never manage control plane instances, etcd backups, or logging agents themselves, and they cannot accidentally break the thing keeping their cluster alive. The same machine images, container images, and operator agent run in both places, with edge-specific behaviors selected by configuration. 

Because it is the same stack, new Kubernetes and EKS platform versions arrive in lockstep with their cloud release, and features like EKS add-ons, Pod Identity, and access entries work the same way they do in a Region.

The hardest part was keeping etcd healthy on hardware with only a few machines that may be cut off from the cloud for days at a time. We solved it by extending the same agent. It keeps a spare copy of the data continuously up to date and promotes it the instant a machine fails, so the cluster heals itself with no human involvement and no connection to the cloud. 

Observability survives the disconnect, too: the metrics agent continues collecting and writing to local disk, shedding the least critical data first when space runs short, so the signals that matter most are the last to go. When the link returns, the buffered data is flushed back with its original timestamps.

All of this only works because the system was designed from the start to operate without anyone logged in. That same design is what makes it possible to deploy changes safely across the entire fleet.

Operating safely at fleet scale

Every one of these changes was deployed to a running fleet of hundreds of thousands of clusters. The journal migration and collocation required transitioning each cluster individually. Every migration follows a strict sequence: validate pre-conditions, create a point-in-time snapshot, perform the switchover, validate post-conditions. If any step fails, the system rolls back automatically. 

Rollouts proceed cell by cell, zone by zone, region by region, with automated monitoring comparing latency, error rates, and throughput between updated and non-updated clusters. Any statistically significant deviation triggers an automatic halt.

What made all of this possible is that EKS is built to operate without human intervention at the individual cluster level. Through Zero Operator Access, the architecture prevents AWS personnel from having technical pathways to access customer content in the managed control plane. A system designed to work without human access must be observable, recoverable, and automatable from the start, and that same discipline is what enables operating at extreme scale.

Three operational lessons shaped how we approach this work.

The first is that a healthy leader is not the same as a working one. The control plane’s controllers run in an active-passive configuration, and early on, we treated an unhealthy standby as if cluster operations had halted. They had not; what matters is whether a leader exists. But the harder lesson: a leader can quietly stop making progress while still renewing its lease and passing every health check. The signal that caught this was watching the controller’s work queue depth. If the queue fills while the leader looks healthy, the system is falling behind in ways no liveness probe will catch.

“A leader can quietly stop making progress while still renewing its lease and passing every health check. The signal that caught this was watching the controller’s work queue depth.”

The second is that maintenance ordering matters as much as the maintenance itself. etcd defragmentation is blocking, and the pause grows with database size. When it hit the leader, every write stalled. We taught the agent to move leadership to a healthy node before defragmenting, so the disruptive work always lands on a follower while writes keep flowing.

The third is that liveness is not readiness. A process can be alive but not ready while it warms caches, and routing based solely on liveness sends requests to an instance that cannot handle them. Equally, readiness flapping during graceful draining should never trigger a restart. We keep the two signals strictly separate: one decides recovery; the other decides routing.

None of this work is visible from the outside, and that is the point. The largest clusters taught us lessons that made every cluster faster. The riskiest migrations produced safety machinery that protects every upgrade. The upstream fixes we contributed for workloads at the edge of what Kubernetes can handle flow back to every user of the project.

“None of this work is visible from the outside, and that is the point.”

When you deploy on EKS and your pods come up in seconds, even during a burst, even when something behind the scenes goes wrong, that speed is not accidental. It is the accumulated result of years of operating at scales where small problems can become big ones fast, and engineering the system to contain them before they do.

To explore the architectures referenced in this post, see EKS Provisioned Control Plane and local Amazon EKS clusters on AWS Outposts.

The post Operating Kubernetes at scale: a few stories from running Amazon EKS appeared first on The New Stack.

Kubernetes teams automate deployments without thinking about it. CI/CD pipelines fire dozens of times a day, autoscaling adjusts replicas in the background, rollback is muscle memory. But there is one category of automation where that confidence vanishes: letting a system change CPU and memory requests on a running workload without a human reviewing it first. 

And as AI inference lands on Kubernetes at scale, that hesitation is becoming hard to ignore, and increasingly expensive.

Why teams trust automation for change but not for constraint

We surveyed 321 Kubernetes practitioners at enterprise organizations earlier this year. The headline finding is one most practitioners will recognize immediately: 82% report high or complete trust in automated delivery controls. But 71% still require human review before applying resource optimization recommendations. Only 27% allow CPU and memory changes to be auto-applied, even within guardrails.

“Deploying code feels additive… rightsizing feels subtractive because you are removing safety margin from a running service, and the failure mode is fundamentally different.”

Those numbers describe a specific asymmetry. The same engineers who deploy to production dozens of times a day without hesitation slow down the moment automation wants to adjust resource allocation. And the survey data make it clear why. Deploying code feels additive. You are shipping new value, the rollback path is well understood, and if something breaks you usually see it right away. Meanwhile, rightsizing feels subtractive because you are removing safety margin from a running service, and the failure mode is fundamentally different.

As one practitioner in the survey put it: “Automated right-sizing carries a unique risk because it directly impacts the underlying stability of the application runtime. Unlike a code deployment that follows a tested path, resource changes alter the invisible contract between the workload and the scheduler.”

When you change resource requests, you change how Kubernetes schedules, prioritizes, and allocates resources. Those effects are not visible the way a code change is. You can’t trace them through a deployment pipeline. And you might not discover that something went wrong until two weeks later, when a traffic spike hits a threshold that didn’t exist at the old values. By that point, three other things have changed too, and proving causation is nearly impossible. The people responsible for those workloads are the same people who get paged at 2 a.m., and they know this.

Why AI workloads raise the stakes

That trust gap existed before inference workloads showed up. What’s changed is the cost of not closing it.

For a long time, teams could absorb the cost of manual oversight. They knew their workloads, had intuition for where the safe boundaries were, and the inefficiency of over-provisioning was a price worth paying for stability. GPU-accelerated inference workloads change that math. GPU compute is significantly more expensive per hour than CPU. The cost of over-provisioning is no longer a rounding error you can absorb quietly. And the workload behavior is less familiar, as inference jobs are bursty in ways teams haven’t built intuition for, traffic patterns shift as models are updated and usage changes, and the resource dimensions involved differ from what teams have spent years learning to tune.

That unfamiliarity compounds with scale. Rightsizing isn’t a one-lever problem the way horizontal scaling is. It involves, at minimum, CPU and memory requests and potentially limits for both, with four dimensions per workload, multiplied across hundreds or thousands of workloads per cluster. The survey data indicates that manual optimization breaks down at around 250 changes a day. Inference workloads push teams past that threshold faster than anything they’ve managed before, because the resource decisions are more frequent and the cost of getting them wrong is higher.

The economic case for automated rightsizing has never been stronger. The organization’s willingness to delegate hasn’t caught up because teams are being asked to trust automation with workloads they don’t yet have a track record with.

What the survey says about closing the gap

When we asked practitioners what would actually increase their trust in optimization automation, 48% said visibility and transparency into how decisions are made, 25% wanted proven guardrails, and 23% needed instant rollback.

Nobody asked for full manual control and very few asked for blind autonomy. What they described is automation that earns trust in stages, and that’s consistent with how the teams furthest along in their automation journey actually got there. They didn’t start with production. They started with a single namespace in a dev environment, observed the system’s behavior, compared recommendations with outcomes, and gradually expanded the scope. Different environments remained at different levels of automation maturity simultaneously, and that was intentional. Production carried more scrutiny than dev.

CI/CD followed the same curve, and the timeline is easy to forget. Most organizations took years to get from running their first automated pipeline to trusting it with production deploys without manual approval on every commit. Kubernetes resource automation is earlier in that same process, and AI workloads are extending the timeline because teams are building trust from scratch with a workload category that doesn’t yet have a track record.

Why automation design matters as much as capability

Some automation architectures deliver meaningful value only with full delegation. The system needs complete control to function the way it was designed to. That’s a form of forced autonomy, and it creates an adoption problem because it asks for exactly the level of trust that most organizations haven’t built yet. Force generally doesn’t work. Teams that feel pushed into a level of delegation they aren’t comfortable with tend to pull back entirely after the first incident.

The alternative is what I’d describe as adaptive autonomy: designing the system to work at every stage of the trust curve. A team still evaluating gets useful recommendations in read-only mode. A team ready to act but wanting boundaries can run guardrailed execution within limits they define. As confidence grows, the system handles more decisions autonomously while humans manage exceptions. And for environments where the track record supports it, closed-loop optimization runs in the background and becomes boring, which is the goal. Each stage is a legitimate operating mode, not a stepping stone you have to rush through.

That design distinction matters more with AI workloads than it ever did with traditional services, precisely because the trust-building process is starting from zero on workloads where the cost of getting it wrong is highest.

“Trust takes a long time to build and a single production incident to undermine.”

The other piece that makes this sustainable is rollout safety. Trust takes a long time to build and a single production incident to undermine. Start with the workloads showing the most headroom between requests and actual usage. Make changes incrementally, small enough that a bad outcome stays contained. Rollback needs to be fast and tied to the health signals the team already monitors. And start with opt-in, not opt-out. Let the teams willing to go first build a track record that others can look at.

The broader pattern

The 71% figure is sometimes read as resistance to automation. I think it’s a more accurate picture of how operational trust actually forms: conditional, earned over time, and moving at different speeds depending on what’s at stake. AI workloads are raising those stakes significantly, which means the path to trusted automation matters more now than it did when the cost of caution was just some unused CPU.

“Most of what gets written about Kubernetes optimization focuses on tooling capability, and the tooling is capable. The harder problem is the human one.”

Most of what gets written about Kubernetes optimization focuses on tooling capability, and the tooling is capable. The harder problem is the human one. If your team is managing AI inference workloads on Kubernetes and your optimization tooling is sitting in read-only mode, the question worth asking isn’t whether to trust the system. It’s whether the system is designed to let you build that trust gradually, starting where the stakes are low and expanding as the evidence supports it, on workloads where getting it wrong costs more than it ever has before.

The post Kubernetes teams trust automation to ship code but not to touch CPU, and AI is raising the stakes appeared first on The New Stack.

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