Glossary

etcd

Kubernetes control-plane state store. An etcd backup captures cluster state; it is not a backup of PostgreSQL data stored on a volume.

Event loop

A mechanism running ready operations and callbacks. Long computation or blocking I/O on its thread delays other work even when the API uses async.

Event Sourcing

ES

Event Sourcing

Storing events as the source of truth from which state can be rebuilt. More than an audit log, it requires versioning, write-conflict handling and replay without repeating external effects.

Event-driven architecture

EDA

Event-Driven Architecture

Components collaborate by publishing and handling events. It requires contracts, duplicate handling and delay diagnosis; it does not automatically imply microservices or event sourcing.

Exactly-once

A single-processing guarantee within an explicitly defined system boundary. Do not assume a broker guarantee includes external payments or arbitrary HTTP effects.

Exception

A signal that interrupts normal execution. Define who handles it, which resources must be released and what state remains after failure.

EXPLAIN

EXPLAIN and ANALYZE are SQL command names, not abbreviations.

A command showing an SQL execution plan. ANALYZE actually executes the query and measures it, so use care with data-changing statements.

External Secrets Operator

ESO

External Secrets Operator

A controller fetching external secret-store data into Kubernetes. It needs its own identity; refreshing a Secret does not guarantee application reload.

Facade

Exposes a simpler operation over collaborating components. It may coordinate availability and pricing; it is not automatically an adapter or a home for every system rule.

Factory Method

An extension point where a subclass chooses an object used by a base-class algorithm. The inheritance cost needs justification.

Fail-fast

A policy stopping an operation after failure instead of executing later steps. It does not automatically undo earlier effects.

fast-check

A JavaScript/TypeScript property-testing library generating inputs and shrinking failures toward simpler examples.

FastAPI

A Python API framework using type information and data validation. Async functions must not perform uncontrolled blocking I/O on the event loop.

FastAPI CLI

CLI

Command-Line Interface

Optional FastAPI application commands including dev and run. Availability depends on installed packages; it is distinct from using Uvicorn directly.

Finalizer

A marker requiring work before Kubernetes object deletion. Stuck deletion needs ownership diagnosis; removing the marker can bypass cleanup.

Floating promise

A promise whose completion or failure is not deliberately handled. The no-floating-promises lint rule detects some cases; void alone does not catch rejection or cancel execution.

Foreign Exchange

FX

Foreign Exchange

Converting between currencies requires an exchange rate, its effective time and a rounding rule. Record these alongside the result; Decimal alone does not choose the correct rate.

Foreign key

FK

Foreign Key

A constraint linking values to a row in another or the same table. It helps preserve relationships; deletion behaviour must be chosen deliberately.

Formatter

A tool normalizing layout and style. It does not replace type checking or behavioral tests.

FrankenPHP

A Caddy-based PHP application server supporting long-lived workers. Serving mode changes application lifecycle; compare modes under the same contract and workload.

Free-threaded Python

An optional CPython build supporting execution without the GIL. Behavior depends on the build and extensions; an extension can require the GIL again. Business synchronization and measurement remain necessary.

Function

A named or anonymous piece of code called with arguments. It returns a result or performs work; identify effects beyond the result that tests must control.

Garbage collection

GC

Garbage Collection

Automatic reclamation of memory of unreachable objects according to runtime rules. It does not close every external resource or fix unnecessary retained references.

Gateway API

Kubernetes resources separating gateway infrastructure from routing rules. GatewayClass selects an implementation, Gateway describes the gateway and HTTPRoute a route. A compatible controller is required.

Generator

A mechanism producing successive values on demand. It can avoid building a complete collection up front; collecting every result into a list or array still uses memory.

Generics

Parameterizing a type with another type, such as a collection’s element type. Variance and runtime checks depend on the language; guarantees differ across stacks.

Git

A version-control system. A commit records repository state and a branch is a movable reference; keep changes small and distinguish code history from learner progress.

Git staging

The Git index holding versions prepared for the next commit. Editing a file after git add does not automatically update its staged version. Read git diff --cached before committing; distinguish the index from an application staging environment.

GitHub CLI (gh)

gh is the GitHub CLI command name, not a separate protocol.

A terminal tool for GitHub authentication, pull requests and releases. It does not replace local Git, and its authentication is independent of your Planapp account. Extracting a ZIP does not require gh.

GitOps

Desired environment state is stored as a versioned declaration. A controller compares it with actual state and reconciles differences. The controller may revert manual changes.