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Cloud · head to head

Fly.io vs K3s

Fly.io logo

Fly.io

Cloud

Deploy web applications globally

From
$29/month
Rated
-
Full reviewWebsite
K3s logo

K3s

Cloud

Lightweight certified Kubernetes distribution in a single binary

From
Free
Rated
-
Full reviewWebsite

The short version

  • Only K3s has a free tier, so it costs nothing to try first.
  • Each has a real cost: Fly.io egress is priced by destination region, from $0.02 per GB in North America and Europe to $0.12 per GB for Africa and India, so the same traffic costs six times more depending on where users are; K3s the SQLite default is single-server only; highly available control planes need etcd or an external datastore, which removes much of the simplicity
  • They diverge on capability: Fly.io covers Global deployment, K3s covers Single binary.

Where they differ

Only the attributes on which Fly.io and K3s actually diverge.

Attributes where Fly.io and K3s differ
AttributeFly.ioK3s
Starting price$29/monthFree
Pricing modelusage-basedOpen source, no licence fee
Free tierNoYes
PlatformsWeb, Api, DockerLinux, ARM, Self-hosted
Founded2020Unknown

Identical on both: user rating (Not yet rated), category (Cloud).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Fly.io

  • Global deployment
  • Docker support
  • Postgres databases
  • Redis support
  • Auto-scaling
  • Health checks
  • Backups
  • Monitoring

Only in K3s

  • Single binary
  • SQLite by default
  • Certified conformant
  • Batteries included
  • Low resource footprint
  • Simple install

What people use each for

The jobs each tool is most often brought in to do.

Fly.io

  • Deploying containerised applications close to users across regionsnot K3s
  • Running full stack apps and databases on managed machinesnot K3s

K3s

  • Kubernetes on edge sites and IoT hardware where full clusters will not fitnot Fly.io
  • Development and CI clusters that must start fast and cost nothingnot Fly.io
  • Small production clusters where full Kubernetes is more operations than the workload justifiesnot Fly.io
  • Teaching and learning Kubernetes without cloud spendnot Fly.io

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Fly.io

  • Egress is priced by destination region, from $0.02 per GB in North America and Europe to $0.12 per GB for Africa and India, so the same traffic costs six times more depending on where users are
  • Stopped machines still bill at $0.15 per GB of root filesystem a month, so a paused service is not a free one
  • Volumes are billed on provisioned capacity rather than usage, at $0.15 per GB a month
  • Reservation discounts of 40% require paying a year up front, from $36 to $1,440
  • Fly Kubernetes is a separate $75 a month per cluster
  • Dedicated IPv4 addresses are $2 a month each

K3s

  • The SQLite default is single-server only; highly available control planes need etcd or an external datastore, which removes much of the simplicity
  • Bundled components such as Traefik are opinionated defaults that larger teams often strip out and replace
  • Removed in-tree cloud provider integrations mean cloud-specific features need external controllers
  • Aimed at small and edge clusters, so very large deployments are better served by a standard distribution

Pricing, plan by plan

Fly.io

$29/month
  • Pay-as-You-Go$null/mo
    • Micro VMs and persistent storage charged by usage
    • FlyCTL CLI
    • Unlimited users and organizations
  • Serious Support$29/month
    • Access to dedicated engineering team
    • All Pay-as-You-Go features
  • Machine Reservation Blocks$null/mo
    • 40% discount on machine usage
    • Requires upfront payment for savings
  • Compliance Package$99/month
    • HIPAA compliance
    • BAAs
    • SOC2 documentation

K3s

Free
  • K3sFree
    • Full functionality
    • No usage limits
    • Community support

Which should you pick?

Choose Fly.io if

  • You need global deployment.
  • You work on Web, Api, Docker.
  • You also want docker support.
Fly.io review

Choose K3s if

  • You need single binary.
  • You want to start without paying.
  • You work on Linux, ARM, Self-hosted.
  • You also want sqlite by default.
K3s review

Questions people ask

Is Fly.io or K3s better?
Neither clearly leads. Fly.io starts at $29/month and K3s at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Fly.io or K3s?
K3s has a free tier; the other does not. Paid plans start at $29/month for Fly.io and Free for K3s.
Does Fly.io or K3s run on more platforms?
Fly.io runs on Web, Api, Docker. K3s runs on Linux, ARM, Self-hosted.
Can I use K3s for free?
Yes. K3s has a free tier, so you can try it without paying. Fly.io starts at $29/month.
What is Fly.io best used for?
Fly.io is most often used for deploying containerised applications close to users across regions, running full stack apps and databases on managed machines. Of those, deploying containerised applications close to users across regions and running full stack apps and databases on managed machines are not what K3s is typically brought in for.
What can Fly.io do that K3s cannot?
Fly.io covers Global deployment, Docker support, Postgres databases, Redis support. K3s covers Single binary, SQLite by default, Certified conformant, Batteries included.

Answered from the vendors’ own pages

Fly.io: Is there a free tier for Fly.io?

Fly.io does not advertise a free tier. The base plan is pay-as-you-go with usage-based pricing for Micro VMs and persistent storage. All users get FlyCTL CLI, unlimited organizations, private networking, SSO, ACLs, and scoped tokens.

Source
K3s: Is K3s free?

Yes. K3s is open source with no licence fee. SUSE sells commercial support around Rancher separately.

Fly.io: How much does Fly.io Serious Support cost?

Serious Support costs 29 USD per month and provides access to a dedicated engineering team while maintaining all pay-as-you-go features for Micro VMs and storage.

Source
K3s: Is K3s real Kubernetes?

Yes. It is CNCF-certified conformant, so standard manifests, kubectl and Helm charts work without modification.

Fly.io: What does Fly.io Compliance Package include?

The Compliance Package is 99 USD per month and includes HIPAA compliance, BAAs, and SOC2 documentation for organizations requiring compliance certifications.

Source
K3s: Why is K3s smaller than Kubernetes?

It strips legacy, alpha and in-tree cloud provider code, packages everything as one binary, and defaults to SQLite instead of etcd.

Fly.io: Does Fly.io offer discounts for upfront commitment?

Yes, Fly.io offers Machine Reservation Blocks with 40% discount on machine usage. This requires upfront payment but applies savings on infrastructure costs.

Source
K3s: Can K3s run in production?

Yes, and it does, particularly at the edge and for small clusters. For a highly available control plane you need to move off the SQLite default to etcd or an external datastore.

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