Concepts

Fission lets you run short-lived functions on Kubernetes without managing pods, deployments, or services yourself. You write a function, point it at a language environment, and bind it to an event with a trigger. Fission turns that into running, autoscaled pods on demand.

This page gives you the mental model. Each object below has its own page that goes deeper.

The four objects you work with

Everything in Fission is built from four core objects, each backed by a Kubernetes Custom Resource:

• A Function is your code plus the configuration that says how to run it.
• An Environment is the language-specific container that builds and runs your function.
• A Trigger binds an event source (an HTTP request, a timer, a message-queue message, a Kubernetes event) to a function invocation.
• A Package holds your code as archives and ties it to an environment, optionally building source into a runnable artifact.

The relationship is simple: a Trigger fires, the request reaches your Function, and your Function runs inside a pod created from its Environment, using the code stored in its Package.

How the objects relate

flowchart TB
  event(["Event Source"]):::user -->|"fires"| trigger["Trigger"]:::fission
  trigger -->|"references"| fn["Function"]:::fission
  fn -->|"references"| env["Environment"]:::fission
  fn -->|"references"| pkg["Package"]:::store
  fn -->|"runs as"| fnPod["Function Pod"]:::pod
  env -->|"runtime image"| fnPod
  pkg -->|"code"| fnPod

  classDef user fill:#ffffff,stroke:#94a3b8,color:#1f2a43
  classDef fission fill:#e8f0fe,stroke:#2d70de,color:#1f2a43
  classDef pod fill:#e6f7f1,stroke:#11a37f,color:#1f2a43,stroke-dasharray:5 3
  classDef store fill:#fff7e0,stroke:#dba514,color:#1f2a43,stroke-dasharray:5 3

A Trigger names a Function. A Function names exactly one Environment and (optionally) one Package. At invocation time Fission combines the Environment’s runtime image with the Package’s code to produce a running Function Pod that serves your request over HTTP.

Explore the concepts

New to Fission? Read the pages in order — they build on each other.

• Functions — what a function is, its entry point and interface, and how invocation works.
• Environments — language runtimes, optional builders, and the versioned environment interface.
• Executors — how Fission provisions and scales function pods (poolmgr vs newdeploy vs container).
• Triggers — the event sources that invoke your functions.
• Packages and builds — source and deployment archives, and the build pipeline.

Specs: declarative configuration

The objects above are normally created with fission CLI commands, but you can also declare them in YAML specs. Specs live on the client side and let the CLI create or update objects idempotently, including bundling your source into archives. See Spec reference for the declarative workflow.

Related

• Architecture — the components that implement these concepts.
• Language environments — the runtimes you can use.