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Azure Functions vs Envoy

Azure Functions logo

Azure Functions

Cloud

Event-driven serverless compute on Azure

From
Free
Free plan
Yes
Visit Azure FunctionsFull review
Envoy logo

Envoy

Developer Tools

A high-performance L7 proxy written in C++ that is configured by an API rather than a config file, and is usually deployed under a control plane.

From
Free
Free plan
Yes
Visit EnvoyFull review

The short version

  • Both are free.
  • Where Azure Functions falls short: the newer Flex Consumption plan's free grant is smaller still, at 250,000 executions and 100,000 GB-seconds per month.
  • Prices and features on this page were last checked on 13 November 2026.

Where they differ

Only the attributes on which Azure Functions and Envoy actually diverge.

Attributes where Azure Functions and Envoy differ
AttributeAzure FunctionsEnvoy
Pricing modelUsage-basedOpen-source
CategoryCloudDeveloper Tools

Identical on both: starting price (Free), free tier (Yes), platforms (Web).

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 Azure Functions

Nothing recorded that Envoy does not also cover.

Only in Envoy

  • xDS dynamic configuration
  • Protocol breadth
  • Filter chain architecture
  • Observability by default
  • Outlier detection
  • Traffic shaping
  • mTLS termination and origination
  • Hot restart

What people use each for

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

Azure Functions

  • Event-driven computingnot Envoy
  • Serverless application backendnot Envoy
  • Scalable API endpointsnot Envoy

Envoy

  • Acting as the data plane under a service mesh or Gateway API implementation, which is how the overwhelming majority of deployments use itnot Azure Functions
  • An edge or API gateway that needs per-route retry budgets, circuit breaking and outlier detection rather than round-robin proxyingnot Azure Functions
  • Migrating traffic between service versions or between a monolith and its replacement, using weighted splits and shadow trafficnot Azure Functions
  • Standardising observability across a polyglot estate, so that latency, error rates and tracing look the same regardless of the language a service is written innot Azure Functions

Where each one falls short

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

Azure Functions

  • Consumption plan free grant is capped at 1 million executions and 400,000 GB-seconds of resource consumption per month per subscription, billed per GB-second beyond that
  • The newer Flex Consumption plan's free grant is smaller still, at 250,000 executions and 100,000 GB-seconds per month
  • Premium plan avoids per-execution charges but bills continuously for allocated core seconds and memory regardless of invocation volume
  • Memory is rounded up to the nearest 128 MB and execution time to the nearest 1 ms for billing, so small overages round upward

Envoy

  • The configuration surface is very large and hand-written bootstrap YAML runs to hundreds of lines for routing that Nginx expresses in twenty, which is why nearly every production deployment sits under a control plane and inherits that control plane's constraints as well
  • xDS is the real API and it is not stable in the comfortable sense; the v2 API set was removed outright, resource types continue to be deprecated, and your control plane and Envoy binaries have to be upgraded roughly in step or the proxies stop accepting configuration
  • Extending it properly means writing a C++ filter and building and maintaining your own Envoy binary; the alternatives are Lua, which adds per-request overhead, and proxy-wasm, whose ABI has remained effectively experimental for years with a real performance cost
  • At sidecar density the per-proxy memory and CPU footprint is a measurable share of cluster capacity, since thousands of workloads each carry a full proxy, and this is precisely the cost that has pushed mesh projects towards node-level or ambient architectures
  • There is no single vendor selling support for Envoy itself; you get the community plus control-plane vendors such as Solo.io and Tetrate, so an Envoy-level production bug is your own engineers in a C++ codebase unless a support contract happens to cover it
  • Diagnosing why a request got a particular response involves reading config dumps, the stats endpoint and the RESPONSE_FLAGS codes in access logs rather than a readable error, which is a specific skill you must hire or spend months growing

Pricing, plan by plan

Azure Functions

Free
  • Consumption PlanOn request
    • 1 million requests free monthly
    • 400,000 GB-seconds free monthly
    • Billed per second and executions
  • Flex Consumption PlanOn request
    • 250,000 executions free monthly
    • 100,000 GB-seconds free monthly
    • Event-driven scaling
  • Premium PlanOn request
    • No execution charges
    • At least one instance required
    • Includes automatic scaling and VNET access

Envoy

Free

No published plan breakdown. See the Envoy review.

Which should you pick?

Choose Azure Functions if

  • You want to start without paying.
Azure Functions review

Choose Envoy if

  • You need xds dynamic configuration.
  • You want to start without paying.
  • You also want protocol breadth.
Envoy review

Questions people ask

Is Azure Functions or Envoy better?
Neither clearly leads. Azure Functions starts at Free and Envoy at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Azure Functions or Envoy?
Azure Functions starts at Free and Envoy at Free.
Does Azure Functions or Envoy run on more platforms?
Both run on Web, so platform support will not decide this one for you.
Can I use Azure Functions for free?
Both have a free tier, so you can try either at no cost before committing.
What is Azure Functions best used for?
Azure Functions is most often used for event-driven computing, serverless application backend, scalable api endpoints. Of those, event-driven computing and serverless application backend are not what Envoy is typically brought in for.
What can Azure Functions do that Envoy cannot?
Envoy covers xDS dynamic configuration, Protocol breadth, Filter chain architecture, Observability by default.

Answered from the vendors’ own pages

Azure Functions: Does Azure Functions have a free tier?

Yes, Azure Functions includes a monthly free grant of 1 million requests and 400,000 GB-seconds on the Consumption Plan, or 250,000 executions and 100,000 GB-seconds on Flex Consumption.

Source
Envoy: Should I run Envoy on its own, or under a control plane?

Almost always under one. Directly authoring xDS or static bootstrap configuration is viable for a handful of routes and becomes unmanageable beyond that. Envoy Gateway, Istio, Contour, Gloo and Consul all exist to generate that configuration for you.

Azure Functions: What is Azure Functions' pricing model?

Azure Functions uses usage-based pricing. Consumption plans charge per second of resource consumption and per execution, measured in gigabyte-seconds and rounded to the nearest 128 MB.

Source
Envoy: How does it compare with Nginx or HAProxy?

Envoy is dynamically configured over an API and instrumented far more heavily; Nginx and HAProxy are faster to configure and lighter for straightforward reverse proxying. If you never need to change routing without a reload, Envoy is more machinery than the problem requires.

Azure Functions: What is the minimum execution time for Azure Functions?

The minimum execution time is 100 milliseconds on Consumption plans. Premium plans charge based on core seconds and allocated memory.

Source
Envoy: What does it cost?

Nothing to licence; it is Apache 2.0 and there is no paid edition. The cost is engineering time and, for most organisations, a commercial control plane or cloud service that packages it.

Envoy: Can I write extensions without C++?

You can write Lua filters or proxy-wasm modules in Rust, Go, C++ or AssemblyScript. Both carry per-request overhead compared with a native filter, and the Wasm path has been slower to stabilise than the project originally projected.

Envoy: Is it a CNCF project?

Yes, it is a graduated CNCF project licensed under Apache 2.0, which means the trademark and governance sit with the foundation rather than with Lyft or any vendor.

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