switchly 0.1.0

Switchly gives you runtime control of your APIs to toggle features, schedule maintenance, enforce rate limits, and perform rollouts without redeploying.

Switchly gives you runtime control of your APIs to toggle features, schedule maintenance, enforce rate limits, and perform rollouts without redeploying.

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[!WARNING] Early Access: switchly is fully functional and ready to use. We're actively building on it and real-world feedback is invaluable. If you have feedback, feature ideas, or suggestions, open an issue.

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Key features

Core (switchly.core)

These features are framework-agnostic and available to any adapter.

Feature	Description
🚩 Feature flags	Boolean, string, integer, float, and JSON flags with targeting rules, user segments, percentage rollouts, prerequisites, and a live evaluation stream. Built on the OpenFeature standard
🚦 Rate limiting	Per-IP, per-user, per-API-key, or global counters with tiered limits, burst allowance, and runtime mutation
⏰ Scheduled windows	asyncio-native scheduler, maintenance windows activate and deactivate automatically
🔔 Webhooks	Fire HTTP POST on every state change. Built-in Slack formatter and custom formatters supported
📋 Audit log	Every state change is recorded: who, when, what route, old status → new status
🖥️ Admin dashboard	HTMX-powered UI with live SSE updates, no JS framework required
🖱️ REST API + CLI	Full programmatic control from the terminal or CI pipelines, works over HTTPS remotely
🏗️ Switchly Server	Centralised control plane for multi-service architectures. SDK clients sync state via SSE with zero per-request latency
🌐 Multi-service CLI	SWITCHLY_SERVICE env var scopes every command; switchly services lists connected services
⚡ Zero-restart control	State changes take effect immediately, no redeployment or server restart needed
🔄 Sync & async	Full support for both async def and plain def route handlers. Use await engine.* or engine.sync.*
🛡️ Fail-open by default	If the backend is unreachable, requests pass through. Switchly never takes down your API
🔌 Pluggable backends	In-memory (default), file-based JSON, or Redis for multi-instance deployments

Framework adapters

FastAPI (switchly.fastapi) ✅ supported

Feature	Description
🎨 Decorator-first DX	@maintenance, @disabled, @env_only, @force_active, @deprecated, @rate_limit. State lives next to the route
📄 OpenAPI integration	Disabled / env-gated routes hidden from /docs; deprecated routes flagged; live maintenance banners in the Swagger UI
🧩 Dependency injection	All decorators work as Depends(), enforcing route state per-handler without middleware
🎨 Custom responses	Return HTML, redirects, or any response shape for blocked routes. Set per-route or as an app-wide default on the middleware
🔀 SwitchlyRouter	Drop-in APIRouter replacement that auto-registers route metadata with the engine at startup

Disabled and env-gated routes hidden from /docs. Maintenance banners injected live.

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Install

uv add "switchly[all]"
# or: pip install "switchly[all]"

Quickstart

We currently support FastAPI. More framework adapters are on the way.

from fastapi import FastAPI
from switchly import make_engine
from switchly.fastapi import (
    SwitchlyMiddleware, SwitchlyAdmin, apply_switchly_to_openapi,
    maintenance, env_only, disabled, force_active, deprecated,
)

engine = make_engine()

app = FastAPI()
app.add_middleware(SwitchlyMiddleware, engine=engine)

@app.get("/payments")
@maintenance(reason="DB migration — back at 04:00 UTC")
async def get_payments():
    return {"payments": []}

@app.get("/health")
@force_active
async def health():
    return {"status": "ok"}

apply_switchly_to_openapi(app, engine)
app.mount("/switchly", SwitchlyAdmin(engine=engine, auth=("admin", "secret")))

GET /payments  → 503  {"error": {"code": "MAINTENANCE_MODE", ...}}
GET /health    → 200  always

Manage routes from the CLI with no code changes or restarts:

switchly config set-url http://localhost:8000/switchly
switchly login admin
switchly status
switchly enable GET:/payments
switchly global enable --reason "Deploying v2" --exempt /health

Admin dashboard — route states, audit log, rate limits, and feature flags. No JS framework required.

Decorators

Decorator	Effect	Status
@maintenance(reason, start, end)	Temporarily unavailable	503
@disabled(reason)	Permanently off	503
@env_only("dev", "staging")	Restricted to named environments	404 elsewhere
@deprecated(sunset, use_instead)	Still works, injects deprecation headers	200
@force_active	Bypasses all switchly checks	Always 200
@rate_limit("100/minute")	Cap requests per IP, user, API key, or globally	429

Custom responses (FastAPI)

By default, blocked routes return a structured JSON error body. You can replace it with HTML, a redirect, plain text, or custom JSON in two ways:

Per-route: pass response= directly on the decorator:

from starlette.requests import Request
from starlette.responses import HTMLResponse, RedirectResponse
from switchly.fastapi import maintenance, disabled

def maintenance_page(request: Request, exc: Exception) -> HTMLResponse:
    return HTMLResponse(
        f"<h1>Down for maintenance</h1><p>{exc.reason}</p>", status_code=503
    )

@router.get("/payments")
@maintenance(reason="DB migration", response=maintenance_page)
async def payments():
    return {"payments": []}

@router.get("/orders")
@maintenance(reason="Upgrade in progress", response=lambda *_: RedirectResponse("/status"))
async def orders():
    return {"orders": []}

Global default: set once on SwitchlyMiddleware, applies to every route without a per-route factory:

app.add_middleware(
    SwitchlyMiddleware,
    engine=engine,
    responses={
        "maintenance": maintenance_page,   # all maintenance routes
        "disabled": lambda req, exc: HTMLResponse(
            f"<h1>Gone</h1><p>{exc.reason}</p>", status_code=503
        ),
    },
)

Resolution order: per-route response= → global responses[...] → built-in JSON. The factory can be sync or async and receives the live Request and the SwitchlyException that triggered the block.

Rate limiting

from switchly.fastapi import rate_limit

@router.get("/public/posts")
@rate_limit("10/minute")               # 10 req/min per IP
async def list_posts():
    return {"posts": [...]}

@router.get("/users/me")
@rate_limit("100/minute", key="user")  # per authenticated user
async def get_current_user():
    ...

@router.get("/reports")
@rate_limit(                           # tiered limits
    {"free": "10/minute", "pro": "100/minute", "enterprise": "unlimited"},
    key="user",
)
async def get_reports():
    ...

Policies can be mutated at runtime without redeploying (switchly rl and switchly rate-limits are aliases):

switchly rl set GET:/public/posts 20/minute   # raise the limit live
switchly rl reset GET:/public/posts           # clear counters
switchly rl hits                              # blocked requests log

Requires switchly[rate-limit]. Powered by limits.

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Feature flags

switchly ships a full feature flag system built on the OpenFeature standard. All five flag types, multi-condition targeting rules, user segments, percentage rollouts, and a live evaluation stream. Managed from the dashboard or CLI with no code changes.

from switchly import (
    FeatureFlag, FlagType, FlagVariation, RolloutVariation,
    TargetingRule, RuleClause, Operator, EvaluationContext,
)

engine.use_openfeature()

# Define a boolean flag with a 20% rollout and individual targeting
await engine.save_flag(
    FeatureFlag(
        key="new-checkout",
        name="New Checkout Flow",
        type=FlagType.BOOLEAN,
        variations=[
            FlagVariation(name="on",  value=True),
            FlagVariation(name="off", value=False),
        ],
        off_variation="off",
        fallthrough=[
            RolloutVariation(variation="on",  weight=20_000),  # 20%
            RolloutVariation(variation="off", weight=80_000),  # 80%
        ],
        targets={"on": ["beta_tester_1"]},   # individual targeting
        rules=[
            TargetingRule(
                description="Enterprise users always get the new flow",
                clauses=[RuleClause(attribute="plan", operator=Operator.IS, values=["enterprise"])],
                variation="on",
            )
        ],
    )
)

# Evaluate in an async route handler
ctx = EvaluationContext(key=user_id, attributes={"plan": user.plan})
enabled = await engine.flag_client.get_boolean_value("new-checkout", False, ctx)

# Evaluate in a sync def handler (thread-safe)
enabled = engine.sync.flag_client.get_boolean_value("new-checkout", False, {"targeting_key": user_id})

Manage flags and segments from the CLI:

switchly flags list
switchly flags eval new-checkout --user user_123
switchly flags disable new-checkout          # kill-switch
switchly flags enable new-checkout
switchly flags stream                        # live evaluation events

switchly segments create beta_users --name "Beta Users"
switchly segments include beta_users --context-key user_123,user_456
switchly segments add-rule beta_users --attribute plan --operator in --values pro,enterprise

Requires switchly[flags].

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Framework support

switchly's core is completely framework-agnostic with zero framework imports. Adapters plug into the engine and expose framework-native patterns like decorators, middleware, and routers.

Framework	Status	Adapter
FastAPI	✅ Supported	switchly.fastapi
More coming	🔜 On the way	—

Want your framework supported? Open an issue.

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Backends

Embedded mode (single service)

Backend	Persistence	Multi-instance	Best for
MemoryBackend	No	No	Development, tests
FileBackend	Yes	No (single process)	Simple single-instance prod
RedisBackend	Yes	Yes	Load-balanced / multi-worker prod

For rate limiting in multi-worker deployments, use RedisBackend. Counters are atomic and shared across all processes.

Switchly Server mode (multi-service)

Run a dedicated SwitchlyServer process and connect each service via SwitchlySDK. State is managed centrally; enforcement happens locally with zero per-request network overhead.

# Switchly Server (centralised, runs once)
from switchly.server import SwitchlyServer
switchly_app = SwitchlyServer(backend=MemoryBackend(), auth=("admin", "secret"))

# Each service (connects to the Switchly Server)
from switchly.sdk import SwitchlySDK
sdk = SwitchlySDK(server_url="http://switchly-server:9000", app_id="payments-service")
sdk.attach(app)

Scenario	Switchly Server backend	SDK rate_limit_backend
Multi-service, single replica each	MemoryBackend or FileBackend	not needed
Multi-service, multiple replicas	RedisBackend	RedisBackend (shared counters)

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Documentation

Full documentation at attakay78.github.io/switchly

Tutorial	Get started in 5 minutes
Decorators reference	All decorator options
Rate limiting	Per-IP, per-user, tiered limits
Feature flags	Targeting rules, segments, rollouts, live events
SwitchlyEngine reference	Programmatic control
Backends	Memory, File, Redis, Switchly Server, custom
Admin dashboard	Mounting SwitchlyAdmin
CLI reference	All CLI commands
Switchly Server guide	Multi-service centralized control
Distributed deployments	Multi-instance backend guide
Production guide	Monitoring & deployment automation

License

MIT