Fly.io vs Heroku

What Fly.io is

Fly.io runs application containers in multiple regions close to users, with a networking layer that makes a multi-region deployment feel like one app. Running the same container in several regions is a configuration choice rather than an architecture project, which matters when latency is the product. In exchange you take on multi-region data questions, since replicating state is still your problem.

What Heroku is

Heroku is a proprietary platform as a service that builds and runs applications in managed dyno containers, with pipelines, logs, data products and marketplace add-ons. Eco provides 1,000 shared personal-account dyno hours for $5 monthly and sleeps inactive web apps; Basic and larger dynos are usage-prorated up to published monthly caps. Dyno filesystems are ephemeral, so durable state belongs in databases or object storage. Compute, data services, add-ons, CI, support and private networking must be costed together.

What Fly.io is built to do

Multi-region deploys

Runs the same application in several regions behind one anycast address.

Machines API

Starts and stops per-request virtual machines programmatically.

Private networking

Connects application instances across regions on a private mesh.

What Heroku is built to do

Managed dynos

Runs isolated application processes with platform-managed cycling and replacement.

Release workflow

Builds deployable releases and supports pipelines, review apps and one-off administrative processes.

Data and add-ons

Attaches Heroku data products and third-party marketplace services to applications.

Runtime tiers

Offers sleeping personal Eco dynos through always-on production and isolated Private/Shield options.

Choose Fly.io if

• Teams with users spread across continents who care about latency.

Choose Heroku if

• Conventional stateless web and worker applications needing fast deployment and managed runtime operations
• Small experiments on Eco where sleep and the shared 1,000-hour pool are acceptable
• Production services after sizing dynos, databases, add-ons, regions and support as one bill

Skip Heroku if

• The application needs persistent local disk, privileged host access or unusual infrastructure control
• Cold starts, a single Eco dyno per process type or hour exhaustion are unacceptable
• Data residency is assumed from the app region without reviewing control-plane and add-on behavior

Fly.io: pros & cons

• Genuinely easy multi-region deployment
• Runs full containers, not a restricted runtime
• Good fit for latency-sensitive workloads
• Multi-region data is still your problem to solve
• Operational rough edges reported by users
• Pricing needs attention once you add regions

Heroku: pros & cons

• Managed runtime: Heroku handles container placement, restarts and underlying operating-system administration.
• Simple release model: Source or container deployments, configuration variables and one-off commands support repeatable application delivery.
• Integrated ecosystem: Pipelines, review apps, Postgres, Key-Value Store and marketplace add-ons reduce integration work.
• Granular billing: Most dynos and data add-ons are prorated to the second up to a monthly maximum.
• No general free compute tier: Eco costs $5 monthly, is personal-app only and can exhaust its shared hour pool.
• Eco cold starts: Inactive web dynos sleep after 30 minutes and wake with a delay.
• Ephemeral local disk: Files written at runtime disappear across restarts, deploys or dyno replacement.
• Stacked cost: Production dynos, databases, add-ons, CI, teams and support can materially exceed the headline compute price.