lambda-framework-go

README

lambda-framework-go

A small framework for AWS Lambda functions written in Go, on Powertools for AWS Lambda (Go): what AWS recommends, done the way AWS recommends it, in a comfortable shape. main.go configures; each handler receives its clients and does its job.

It wires the Powertools logger, tracer and metrics, the Powertools Event Handler router with typed, validated operations, the AWS SDK clients and a database pool, to Postgres or to Aurora DSQL, around your business handlers, and gives every failure one place to be reported.

Requires Go 1.27.

go get github.com/alessandrolattao/lambda-framework-go

Packages

Package	What it does
framework	Container with the dependencies; Get/Post/Put/Patch/Delete and HTTP for API Gateway HTTP APIs; Handle and Consume for every other event; error and panic reporting
request	What typed binding does not cover: the JWT claims API Gateway verified, the client IP behind trusted proxies, comma-separated id lists
response	The error envelope, success responses with cache headers, CSV and content negotiation

Quick start

An HTTP API

package main

import (
	"context"
	"errors"
	"uuid"

	"github.com/aws/aws-lambda-go/lambda"
	"github.com/jackc/pgx/v5"

	"github.com/alessandrolattao/lambda-framework-go/framework"
	"github.com/alessandrolattao/lambda-framework-go/response"
)

func main() {
	c := framework.New()
	c.Get("/orders/{id}", getOrder)
	lambda.Start(c.HTTP())
}

// orderID is what the route reads; the router binds and validates it.
type orderID struct {
	ID uuid.UUID `path:"id" format:"uuid"`
}

type order struct {
	ID    uuid.UUID `json:"id"`
	Total int64     `json:"total"`
}

func getOrder(ctx context.Context, c *framework.Container, in orderID) (order, error) {
	o := order{ID: in.ID}
	err := c.DB.QueryRow(ctx, "SELECT total FROM orders WHERE id = $1", in.ID).Scan(&o.Total)
	if errors.Is(err, pgx.ErrNoRows) {
		return order{}, response.NotFound("orderNotFound", "no order with this id", nil)
	}
	if err != nil {
		return order{}, response.InternalServerError(err, "serverError", "could not read the order", nil)
	}
	return o, nil
}

Input structs follow the Powertools Event Handler: fields tagged path, query, header, cookie, a Body field decoded from JSON, constraints as tags (minimum, maxLength, pattern, enum, format, required...). A request that does not conform never reaches the handler: it gets a 422. The same types describe the API: c.Router().OpenAPIJSON() is its OpenAPI document.

Any other event

Handlers that only succeed or fail (EventBridge, SQS, S3, CloudWatch Logs) use Consume; handlers that answer with a result use Handle:

lambda.Start(c.Consume(func(ctx context.Context, c *framework.Container, e events.SQSEvent) error {
	// ...
	return nil
}))

The other Powertools utilities (batch, idempotency, parameters, feature flags, validation, parser...) work inside these handlers as they do anywhere.

What happens around a handler

• The Powertools decorators, stacked as Powertools recommends. The logger's InjectContext (Lambda context keys, correlation id for API Gateway, ALB, Function URL and EventBridge events, sampling, buffering), the tracer's CaptureLambdaHandler (the invocation span, ColdStart and Service annotations) and, when metrics are configured, LogMetrics (one metric set per invocation, flushed at its end).
• Initialization once per cold start. The AWS config, the clients (S3, EventBridge, SFN, Dynamo, Websocket) and the database pool (Postgres or Aurora DSQL) are created on the first invocation and reused afterwards. A failed initialization is retried by the next invocation. A client you put in a field before that (a fake, in a test) is kept.
• Per-invocation state in the context. The handler shares the container, which is read-only once initialized; the request id, the client's address (client_ip) and the metric set live in the context. Log with the Context methods (c.Logger.InfoContext(ctx, ...)) and the records carry them, also when one execution environment runs several invocations at once (Lambda Managed Instances).
• One door for failures. Return the error and log nothing: the framework writes it once, at Error, with the request id. Wrap the context only the handler knows into the error (fmt.Errorf("charge order %v: %w", id, err)). A panic is written down with its stack.
• Failures Lambda can tell apart. A failure reaches Lambda (and Step Functions, which matches Retry and Catch rules on it) with an errorType that means something: the type of the application's or library's error in the chain (PgError, ...), or HandlerError, InvalidEvent, InvalidResult, InitError. aws-lambda-go's own plain text copy of the failure goes to Debug.
• Every API request leaves a line. API request completed carries the status, the route and the duration, so a 404 or a 422 is visible too.
• API Gateway always gets an answer, in one envelope. A *response.Error answers with {"code","message","details","timestamp"}; so do the router's own errors: an unknown route (routeNotFound), a request that fails validation (invalidParam, invalidBody, with the Powertools details), an unsupported content type, a Powertools ServiceError. A failure no handler answered becomes a 500 serverError. A 5xx is reported once, with its cause, which never reaches the client. Lambda counts such invocations as successes, so alarm on the error logs rather than on the Errors metric.
• JSON v2 both ways. Events are decoded and results encoded with encoding/json/v2; response bodies with sorted map keys.
• Tracing with OpenTelemetry, through the Powertools tracer: the X-Ray UDP exporter the AWS X-Ray migration guide prescribes for Lambda. Each invocation is a server span under the trace Lambda started, the handler runs in a ## businessLogic span, and the AWS SDK calls and the database queries (through otelpgx: operation and SQL text, never the parameters) made with its context are spans below it. An API request is described on the invocation's span (X-Ray's http block, http_route and http_status annotations); a 5xx marks both spans as failed. Open your own spans with c.Tracer.Capture(ctx, name, fn). Turn on active tracing on the function: without an X-Ray endpoint, tracing is off.

Configuration

Options of framework.New:

Option	Default	Meaning
WithService(name)	POWERTOOLS_SERVICE_NAME, else the function name	The service of the logs, the traces and the metrics
WithLogging(opts...)		Options of the Powertools logger (level, sampling, buffering, format)
WithTracing(opts...)		Options of the Powertools tracer
WithTracerProvider(tp)	X-Ray UDP exporter	Another OpenTelemetry tracer provider
WithMetrics(opts...)	off	Turns the Powertools metrics on (namespace, dimensions, Datadog)
WithRouter(opts...)		Options of the Event Handler router (CORS, debug, strip prefixes, OpenAPI)
WithDatabaseURL(url)	DATABASE_URL	Postgres connection string
WithDSQLEndpoint(endpoint)	DSQL_ENDPOINT	Aurora DSQL cluster endpoint, in the region in AWS_REGION
WithTrustedProxies(n)	0	Proxies in front of API Gateway (CloudFront is 1), used to find the client IP

Environment variables: every POWERTOOLS_* variable of the utilities (POWERTOOLS_SERVICE_NAME, POWERTOOLS_LOG_LEVEL, POWERTOOLS_LOGGER_SAMPLE_RATE, POWERTOOLS_METRICS_NAMESPACE, POWERTOOLS_TRACE_DISABLED, POWERTOOLS_DEV for indented logs while developing...), Lambda's AWS_LAMBDA_LOG_LEVEL, and:

Variable	Meaning
DATABASE_URL	Postgres connection string, when WithDatabaseURL is not used
DSQL_ENDPOINT	Aurora DSQL cluster endpoint, when WithDSQLEndpoint is not used
AWS_REGION	The region of the Aurora DSQL cluster; Lambda sets it to the function's own
WS_ENDPOINT	WebSocket API endpoint; without it Websocket is nil
AWS_ENDPOINT_URL, AWS_ENDPOINT_URL_S3	A custom S3 endpoint (MinIO, LocalStack, Floci); S3 then uses path-style addressing

Metrics are on when WithMetrics is used or POWERTOOLS_METRICS_NAMESPACE is set; without them no invocation flushes an empty metric set.

A container has at most one database: Postgres with a connection string, Aurora DSQL with a cluster endpoint. With neither there is no pool and DB is nil; with both, the first invocation fails. Either way DB is a *pgxpool.Pool, and handlers use it the same way.

Postgres

The Postgres pool holds one connection per invocation the execution environment can run at once, unless the connection string sets pool_max_conns. Every statement is capped to the time the invocation has left.

Aurora DSQL

DSQL has no password: a connection authenticates with an IAM token. The pool goes through AWS's own connector, Aurora DSQL Connector for Go on pgx, which signs a fresh token, valid 15 minutes, for every new connection with the function's credentials. A warm execution environment that opens a connection long after its cold start still gets in.

• The pool connects to the postgres database as the database user admin, over TLS verified against the endpoint. The function's role needs dsql:DbConnectAdmin on the cluster.
• It holds one connection per invocation the execution environment can run at once, and recycles them with the connector's own lifetimes (55 minutes, 10 minutes idle), below the hour after which DSQL closes a connection.
• Statements are not capped server side: DSQL rejects statement_timeout and ends every transaction after 5 minutes on its own. A query still running when the invocation's deadline passes fails at that deadline, on the client.
• Queries run in pgx's QueryExecModeDescribeExec, as the connector sets it: safe across live schema changes, at the cost of one more round trip per query.
• DSQL resolves conflicting transactions with optimistic concurrency control: the transaction that commits second fails with SQLSTATE OC000, OC001 or 40001, and is meant to be retried. The connector's occretry package retries a transaction or a statement on c.DB.

With SST

SST encrypts linked resources into the function bundle, so the database password never sits in a plaintext environment variable. Keep it that way: read the linked resource in main and pass the connection string.

Postgres

import (
	"fmt"
	"net"
	"net/url"

	"github.com/sst/sst/v3/sdk/golang/resource"
)

func databaseURL() (string, error) {
	get := func(key string) (string, error) {
		v, err := resource.Get("Database", key)
		if err != nil {
			return "", err
		}
		return fmt.Sprint(v), nil
	}
	host, err := get("host")
	if err != nil {
		return "", err
	}
	port, _ := get("port")
	user, _ := get("username")
	password, _ := get("password")
	name, _ := get("database")

	u := url.URL{
		Scheme: "postgres",
		User:   url.UserPassword(user, password),
		Host:   net.JoinHostPort(host, port),
		Path:   "/" + name,
	}
	return u.String(), nil
}

func main() {
	dsn, err := databaseURL()
	if err != nil {
		panic(err)
	}
	c := framework.New(framework.WithDatabaseURL(dsn))
	c.Get("/orders/{id}", getOrder)
	lambda.Start(c.HTTP())
}

Aurora DSQL

Link the cluster to the function: the link carries the endpoint and grants the function's role dsql:DbConnect and dsql:DbConnectAdmin on the cluster.

const database = new sst.aws.Dsql("Database");

new sst.aws.Function("Orders", {
  handler: "./cmd/orders",
  runtime: "go",
  link: [database],
});

Read the endpoint in main and pass it on; the region is the function's own, in AWS_REGION.

import (
	"fmt"

	"github.com/sst/sst/v3/sdk/golang/resource"
)

func main() {
	endpoint, err := resource.Get("Database", "endpoint")
	if err != nil {
		panic(err)
	}
	c := framework.New(framework.WithDSQLEndpoint(fmt.Sprint(endpoint)))
	c.Get("/orders/{id}", getOrder)
	lambda.Start(c.HTTP())
}

Testing a handler

Build a Container by hand with fakes in its fields and call the business handler directly: a hand-built container is never initialized behind your back, and it does not trace.

c := &framework.Container{Logger: logging.New(logging.WithWriter(io.Discard)), EventBridge: fakeBus}
got, err := getOrder(t.Context(), c, orderID{ID: id})

To go through the framework as well, routing and validation included, call the Lambda handler with an event: c.HTTP().Call(ctx, request), or c.Handle(h).Call(ctx, event).

Development

go test ./...
golangci-lint run ./...

The lint configuration is strict, the same as Powertools'. The Aurora DSQL tests need neither a cluster nor the network: the pool connects lazily, and they sign tokens with fixed credentials. The Postgres tests skip themselves without a database. To run them:

docker run -d --rm -e POSTGRES_PASSWORD=postgres -p 55432:5432 postgres:18-alpine
TEST_DATABASE_URL='postgres://postgres:postgres@localhost:55432/postgres?sslmode=disable' go test ./...

The parsers that read what a client sends have fuzz tests; go test runs their seeds, and fuzzing one goes like this:

go test -run '^$' -fuzz '^FuzzClientIP$' -fuzztime 1m ./request

End-to-end tests

e2e/ is a module of its own (so its test dependencies stay out of this one) that runs two real Lambdas, an API Gateway HTTP API one and an EventBridge one, the way Lambda does: built for provided.al2023, run in the Lambda base image under the Runtime Interface Emulator, with the memory and the CPU share of a Lambda size. Postgres runs next to them (Aurora DSQL has no local version, so the suite runs on Postgres), and a UDP listener stands in for the X-Ray endpoint, so the tests check responses, database writes, log records and exported spans, on the happy paths and the failing ones. It needs Docker.

cd e2e
go test -run TestOrders ./...   # behaviour, about 15 s
go test ./...                   # plus startup times at 128, 512 and 1024 MB, about 100 s

TestStartup measures five cold starts per size and fails when the median cold invocation goes over its limit. E2E_MAX_COLD_START_SCALE=2 doubles the limits on a slower machine; E2E_STARTUP_REPORT=startup.md writes the table of measurements to a file.

License

MIT, see LICENSE.