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fix: use alias for versioned lambda functions #6767

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fix: use alias for versioned lambda functions #6767

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0e3e96d
Route versioned functions through a stable alias
anatolzak Apr 18, 2026
207829d
fix
anatolzak Apr 19, 2026
0a7d668
Compute targetArn and qualifier lazily via getters
anatolzak May 1, 2026
5f2231e
Respect explicit versioning: false on durable functions
anatolzak May 1, 2026
1e105c1
Inline args.url in normalizeUrl
anatolzak May 1, 2026
6cf7667
feat(function): allow transforming the LatestAlias resource
anatolzak May 1, 2026
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157 changes: 107 additions & 50 deletions platform/src/components/aws/function.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1309,6 +1309,12 @@ export interface FunctionArgs {
/**
* Enable versioning for the function.
*
* :::caution
* If you're wiring this function to an event source by passing its ARN,
* use `fn.targetArn` rather than `fn.arn`. Using `fn.arn` invokes
* `$LATEST` and bypasses the alias that routes to the published version.
* :::
*
* :::note
* Durable functions enable this by default.
* :::
Expand Down Expand Up @@ -1476,6 +1482,12 @@ export interface FunctionArgs {
* This property is meant to be used internally by [Workflow](/docs/component/aws/workflow).
* Prefer the component if you want to use the [SDK](/docs/component/aws/workflow#sdk) or if you are not very familiar with durable functions limitations.
* :::
*
* :::caution
* If you're wiring this function to an event source by passing its ARN,
* use `fn.targetArn` rather than `fn.arn`. Using `fn.arn` invokes
* `$LATEST` and bypasses the alias that routes to the published version.
* :::
*/
durable?:
| boolean
Expand Down Expand Up @@ -1712,6 +1724,10 @@ export class Function extends Component implements Link.Linkable {
private logGroup: Output<cloudwatch.LogGroup | undefined>;
private urlEndpoint: Output<string | undefined>;
private eventInvokeConfig?: lambda.FunctionEventInvokeConfig;
private alias: Output<lambda.Alias | undefined>;
private isVersioningEnabled: Output<boolean>;
#targetArn: Output<string>;
#qualifier: Output<string | undefined>;

private static readonly encryptionKey = lazy(
() =>
Expand Down Expand Up @@ -1765,7 +1781,7 @@ export class Function extends Component implements Link.Linkable {
const streaming = normalizeStreaming();
const logging = normalizeLogging();
const volume = normalizeVolume();
const url = normalizeUrl();
const url = normalizeUrl(args.url);
const copyFiles = normalizeCopyFiles();
const durable = normalizeDurable();
const policies = output(args.policies ?? []);
Expand All @@ -1781,7 +1797,13 @@ export class Function extends Component implements Link.Linkable {
const logGroup = createLogGroup();
const zipAsset = createZipAsset();
const fn = createFunction();
const urlEndpoint = createUrl();
const isVersioningEnabled = fn.publish.apply((publish) => Boolean(publish));
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@vimtor vimtor Apr 29, 2026

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you can also define versioning with versioning: true

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@anatolzak anatolzak May 1, 2026

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@vimtor fn.publish is the resolved truth on the underlying aws.lambda.Function. Upstream at function.ts:2659, it's set to args.versioning || Boolean(args.durable), so checking fn.publish covers both paths in one expression

const alias = createLatestAlias();
const targetArn = createTargetArn(alias);
const qualifier = output(targetArn).apply(
(arn) => splitQualifiedFunctionArn(arn).qualifier,
);
const urlEndpoint = createLatestUrl();
createProvisioned();
const eventInvokeConfig = createEventInvokeConfig();

Expand All @@ -1792,6 +1814,10 @@ export class Function extends Component implements Link.Linkable {
this.logGroup = logGroup;
this.urlEndpoint = urlEndpoint;
this.eventInvokeConfig = eventInvokeConfig;
this.alias = alias;
this.#targetArn = targetArn;
this.#qualifier = qualifier;
this.isVersioningEnabled = isVersioningEnabled;

const buildInput = output({
functionID: name,
Expand Down Expand Up @@ -1967,8 +1993,8 @@ export class Function extends Component implements Link.Linkable {
}));
}

function normalizeUrl() {
return output(args.url).apply((url) => {
function normalizeUrl(url: FunctionArgs["url"]) {
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@vimtor vimtor Apr 29, 2026

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the normalize function usually don't take arguments

return output(url).apply((url) => {
if (url === false || url === undefined) return;
if (url === true) {
url = {};
Expand Down Expand Up @@ -2002,6 +2028,7 @@ export class Function extends Component implements Link.Linkable {
};
});
}
type NormalizedUrl = ReturnType<typeof normalizeUrl>;
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i don't think we need this


function normalizeCopyFiles() {
return output(args.copyFiles ?? []).apply((copyFiles) =>
Expand Down Expand Up @@ -2630,7 +2657,7 @@ export class Function extends Component implements Link.Linkable {
layers: args.layers,
tags: args.tags,
publish: output(args.versioning).apply(
(v) => v ?? Boolean(args.durable),
(v) => v || Boolean(args.durable),
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why did we change this?

),
reservedConcurrentExecutions: concurrency?.reserved,
durableConfig: durable && {
Expand Down Expand Up @@ -2700,7 +2727,33 @@ export class Function extends Component implements Link.Linkable {
);
}

function createUrl() {
function createLatestAlias() {
return isVersioningEnabled.apply((isVersioningEnabled) => {
if (!isVersioningEnabled) return;

return new lambda.Alias(
`${name}LatestAlias`,
{
functionName: fn.name,
functionVersion: fn.version,
},
{ parent },
);
});
}

function createTargetArn(alias: Input<lambda.Alias | undefined>) {
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this is weird because it's not creating anything. that's why i said to use the getter directly in a comment below

return output(alias).apply((alias) => {
if (alias) return alias.arn;
return fn.arn;
});
}

type CreateUrlOpts = {
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inline types like this are very weird

qualifier: string | undefined;
url: NormalizedUrl;
};
function createUrl({ url, qualifier }: CreateUrlOpts) {
return url.apply((url) => {
if (url === undefined) return output(undefined);

Expand All @@ -2712,23 +2765,10 @@ export class Function extends Component implements Link.Linkable {
([oac, authorization]) => oac || authorization === "iam",
);

/**
* Lambda Function URLs only accept alias names in the explicit `qualifier`
* field. Durable functions with URLs therefore need an alias target here,
* even when the underlying function is still on `$LATEST`.
* See https://github.com/hashicorp/terraform-provider-aws/issues/31459
*/
const qualifier = durable
? new lambda.Alias(`${name}Durable`, {
functionName: fn.arn,
functionVersion: fn.version,
}).name
: undefined;

const fnUrl = new lambda.FunctionUrl(
`${name}Url`,
{
functionName: durable ? fn.arn : fn.name,
functionName: fn.name,
qualifier,
authorizationType: isIam.apply((isIam) =>
isIam ? "AWS_IAM" : "NONE",
Expand All @@ -2738,7 +2778,7 @@ export class Function extends Component implements Link.Linkable {
),
cors: url.cors,
},
{ parent },
{ parent, deleteBeforeReplace: false },
);

if (!url.route) {
Expand All @@ -2750,6 +2790,7 @@ export class Function extends Component implements Link.Linkable {
{
action: "lambda:InvokeFunctionUrl",
function: fn.name,
qualifier,
principal: "*",
functionUrlAuthType: "NONE",
},
Expand All @@ -2760,6 +2801,7 @@ export class Function extends Component implements Link.Linkable {
{
action: "lambda:InvokeFunction",
function: fn.name,
qualifier,
principal: "*",
invokedViaFunctionUrl: true,
},
Expand All @@ -2778,6 +2820,7 @@ export class Function extends Component implements Link.Linkable {
{
action: "lambda:InvokeFunctionUrl",
function: fn.name,
qualifier,
principal: "cloudfront.amazonaws.com",
sourceArn: distributionArn,
},
Expand All @@ -2788,6 +2831,7 @@ export class Function extends Component implements Link.Linkable {
{
action: "lambda:InvokeFunction",
function: fn.name,
qualifier,
principal: "cloudfront.amazonaws.com",
sourceArn: distributionArn,
invokedViaFunctionUrl: true,
Expand All @@ -2800,6 +2844,7 @@ export class Function extends Component implements Link.Linkable {
{
action: "lambda:InvokeFunctionUrl",
function: fn.name,
qualifier,
principal: "*",
functionUrlAuthType: "NONE",
},
Expand All @@ -2810,6 +2855,7 @@ export class Function extends Component implements Link.Linkable {
{
action: "lambda:InvokeFunction",
function: fn.name,
qualifier,
principal: "*",
invokedViaFunctionUrl: true,
},
Expand Down Expand Up @@ -2886,6 +2932,15 @@ export class Function extends Component implements Link.Linkable {
});
}

function createLatestUrl() {
return qualifier.apply((qualifier) =>
createUrl({
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@vimtor vimtor Apr 29, 2026

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we should inline the createUrl function

or keep the createUrl, remove this createLatestUrl and move the logic to the existing method

url,
qualifier,
}),
);
}

function createProvisioned() {
return all([args.concurrency, fn.publish]).apply(
([concurrency, publish]) => {
Expand Down Expand Up @@ -2952,6 +3007,10 @@ export class Function extends Component implements Link.Linkable {
* The Function Event Invoke Config resource if retries are configured.
*/
eventInvokeConfig: this.eventInvokeConfig,
/**
* The Lambda Alias. Available when `versioning` or `durable` is enabled.
*/
alias: this.alias,
};
}

Expand Down Expand Up @@ -2983,46 +3042,42 @@ export class Function extends Component implements Link.Linkable {
return this.function.arn;
}

/** @internal */
private get useQualifiedTarget() {
return this.function.publish.apply(
(publish) => (publish ?? false) || this.durable,
);
}

/** @internal */
/**
* The ARN to use when wiring this function to an event source.
*
* When versioning is enabled, this points to the Lambda alias that routes
* to the currently published version. Otherwise it falls back to the
* function ARN.
*
* Prefer this over `arn` when passing the function to an event source, so
* invocations go through the alias instead of `$LATEST`.
*/
public get targetArn() {
return this.useQualifiedTarget.apply((useQualifiedTarget) =>
useQualifiedTarget ? this.function.qualifiedArn : this.arn,
);
return this.#targetArn;
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why don't define targetArn here instead of adding this #targetArn?

}

/** @internal */
public get qualifier() {
return this.targetArn.apply(
(arn) => splitQualifiedFunctionArn(arn).qualifier,
);
return this.#qualifier;
}

/** @internal */
public get targetInvokeArn() {
return this.useQualifiedTarget.apply((useQualifiedTarget) =>
useQualifiedTarget
? this.function.qualifiedInvokeArn
: this.function.invokeArn,
return this.alias.apply((alias) =>
alias ? alias.invokeArn : this.function.invokeArn,
);
}

/** @internal */
public get targetResponseStreamingInvokeArn() {
return this.useQualifiedTarget.apply((useQualifiedTarget) =>
useQualifiedTarget
return this.alias.apply((alias) =>
alias
? all([
this.arn,
this.function.qualifiedArn,
alias.arn,
this.function.responseStreamingInvokeArn,
]).apply(([arn, qualifiedArn, responseStreamingInvokeArn]) =>
responseStreamingInvokeArn.replace(arn, qualifiedArn),
]).apply(([arn, aliasArn, responseStreamingInvokeArn]) =>
responseStreamingInvokeArn.replace(arn, aliasArn),
)
: this.function.responseStreamingInvokeArn,
);
Expand Down Expand Up @@ -3110,11 +3165,7 @@ export class Function extends Component implements Link.Linkable {
properties: {
name: this.name,
url: this.urlEndpoint,
...(this.durable
? {
qualifier: this.qualifier,
}
: {}),
qualifier: this.qualifier,
},
include: [
permission({
Expand All @@ -3132,7 +3183,13 @@ export class Function extends Component implements Link.Linkable {
]
: []),
],
resources: [this.durable ? interpolate`${this.arn}:*` : this.arn],
resources: this.isVersioningEnabled.apply((isVersioningEnabled) =>
this.durable
? [interpolate`${this.arn}:*`]
: isVersioningEnabled
? [this.arn, interpolate`${this.arn}:*`]
: [this.arn],
),
}),
],
};
Expand Down
7 changes: 6 additions & 1 deletion platform/src/components/aws/workflow.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -272,7 +272,12 @@ export interface WorkflowArgs
* ID generation inside durable operations like `ctx.step()`.
*
* :::caution
* Workflow handlers have versioning enabled. Deploying an update won't update existing running workflows.
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we should keep the versioned behaviour. i don't understand why we changed this

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@anatolzak anatolzak May 1, 2026 •
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@vimtor The versioned behavior is unchanged. The main reason durable workflows version the handler is so that an in-flight execution resumes on the same code it started on. That's preserved: the lanbda API captures the resolved version at execution start and pins all resumes/retries to that captured version, regardless of whether the alias is later moved.

What the alias buys us, beyond what a pinned numeric version gives, is decoupling the handler identity from the deployed version. If you ship a bad release and need to roll back, you just point the alias at the previous version, and no consumers have to be updated. Any newly-started executions immediately run against the rolled-back version. With a pinned qualifiedArn, every consumer (URL, event sources, API GW, SDK qualifier, etc.) would have to be re-wired to roll back.

It also opens the door to weighted aliases: you can split traffic across two versions of a workflow handler for A/B tests or canary rollouts without touching any client. None of that is possible if consumers point at a specific numeric version.

The doc rewrite just makes the mechanism explicit and adds the $LATEST escape hatch. No behavior regression.

* The workflow SDK invokes the handler through an alias. Each execution is pinned
* to the version the alias points to when it starts, and stays pinned across resumes
* and retries — so deploying an update won't affect already-running workflows.
*
* To resume on the latest code, invoke the function directly via the Lambda SDK
* with the `$LATEST` qualifier. Not recommended for production.
* :::
*
* Before using workflows in production, review the
Expand Down
1 change: 1 addition & 0 deletions platform/src/components/component.ts
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Expand Up @@ -147,6 +147,7 @@ export class Component extends ComponentResource {
"aws:cognito/identityPoolRoleAttachment:IdentityPoolRoleAttachment",
"aws:cognito/identityProvider:IdentityProvider",
"aws:cognito/userPoolClient:UserPoolClient",
"aws:lambda/alias:Alias",
"aws:lambda/eventSourceMapping:EventSourceMapping",
"aws:lambda/functionEventInvokeConfig:FunctionEventInvokeConfig",
"aws:lambda/functionUrl:FunctionUrl",
Expand Down
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