Tenant data isolation in Forge apps

Forge apps run in a multi-tenant environment where the same runtime process can serve multiple Atlassian customers (tenants). This means module-level variables and in-memory caches are shared across tenant invocations unless you explicitly scope data to a single invocation.

This guide explains the risk, shows unsafe and safe code patterns, and provides actionable checklists for auditing your app.

Why this happens

The Forge runtime is built on AWS Lambda. Lambda optimizes performance by reusing warm execution environments (process containers) across multiple invocations. When a warm environment is reused:

• The Node.js module cache is not cleared between invocations.
• Any variable declared at module scope retains its value from the previous invocation.
• If the previous invocation belonged to a different tenant, that tenant's data is now visible in the new invocation's scope.

This is a standard characteristic of serverless runtimes, not a Forge-specific bug. However, it conflicts with the intuitive assumption that each function call starts with a clean slate.

Unsafe patterns

The following patterns all share the same root cause: mutable state is declared at module scope and updated during a handler invocation. Because Forge reuses warm execution environments, that state survives into the next invocation, which may belong to a completely different tenant.

Module-level cache

The following pattern is common in Node.js but is unsafe in Forge because cache persists across invocations that may belong to different tenants.

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// UNSAFE: module-level cache shared across all tenants
const cache = {};

export async function handler(context) {

  if (cache['currentUser']) {
    // This could return another tenant's user data!
    return cache['currentUser'];
  }

  const response = await api.asUser().requestJira('/rest/api/3/myself');
  const user = await response.json();

  cache['currentUser'] = user; // Leaks to the next invocation
  return user;
}

Why it's unsafe: If this warm process is reused for a different tenant's invocation, cache['currentUser'] still holds the previous tenant's user object.

Shared mutable object

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// UNSAFE: shared object that accumulates data from multiple tenants
const issueCache = {};

export async function onIssueCreated({ payload, context }) {
  // Issue keys are NOT globally unique - the same key can exist
  // in different tenants' Jira instances
  issueCache[payload.issue.key] = payload.issue;
}

Safe patterns

Each pattern below eliminates the risk in a different way: avoiding module-level state entirely, scoping it to a tenant identifier, or delegating persistence to Forge Storage, which is tenant-scoped by design.

Scope all data to the invocation context

The safest approach is to never store tenant data in module-level variables. Compute or fetch everything within the handler function itself.

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// SAFE: all state is local to the function invocation
export async function handler(context) {
  // Fetch fresh data every invocation - no cross-tenant risk
  const response = await api.asUser().requestJira('/rest/api/3/myself');
  const user = await response.json();
  return user;
}

Partition a cache by tenant identifier

If you need in-process caching for performance, always key the cache by a tenant-specific identifier, such as cloudId. This ensures that a warm process reused for tenant B will only find tenant B's data.

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// SAFE: cache partitioned by cloudId (tenant identifier)
const cache = {};

export async function handler(context) {
  const { cloudId } = context;

  if (cache[cloudId]?.currentUser) {
    return cache[cloudId].currentUser;
  }

  const response = await api.asUser().requestJira('/rest/api/3/myself');
  const user = await response.json();

  // Scope the cached value to this specific tenant
  if (!cache[cloudId]) {
    cache[cloudId] = {};
  }
  cache[cloudId].currentUser = user;

  return user;
}

Use Forge Storage for durable cross-invocation data

Forge hosted storage capabilities (Key-Value Store, Custom Entity Store, SQL, and Object Store) are automatically scoped per app installation, which means they are inherently tenant-safe. Prefer storage over in-memory caches when you need data to persist across invocations.

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import { kvs } from '@forge/kvs';

// SAFE: Forge Storage is scoped per installation (per tenant)
export async function handler(context) {
  const cachedUser = await kvs.get('currentUser');
  if (cachedUser) {
    return cachedUser;
  }

  const response = await api.asUser().requestJira('/rest/api/3/myself');
  const user = await response.json();

  await kvs.set('currentUser', user);
  return user;
}

Use read-only module-level constants

Module-level state that is read-only and not tenant-specific is safe.

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// SAFE: read-only configuration constant - not tenant data
const MAX_RETRIES = 3;
const API_VERSION = 'v3';

export async function handler(context) {
  // MAX_RETRIES and API_VERSION are the same for all tenants
  // and are never modified
}

Audit checklist

Use this checklist to review your Forge app for data isolation risks:

• No mutable module-level variables hold tenant-specific data (user info, issue data, tenant settings, etc.).
• All in-memory caches are keyed by a tenant identifier such as cloudId or installationId.
• Issue keys, page IDs, and other Atlassian identifiers are not used as global cache keys — they are not unique across tenants.
• Durable data that must persist across invocations uses Forge Storage rather than in-memory state.
• Module-level constants are read-only and contain no tenant-specific information.
• Third-party SDK instances (e.g., database clients, HTTP clients initialized with tenant credentials) are not stored at module scope without tenant-scoping.

Static analysis and linting

Forge does not currently provide built-in lint rules to detect unsafe global state. However, you can configure your own ESLint rules to flag patterns that are commonly associated with cross-tenant data leaks:

• Mutable let or var declarations at module scope.
• Assignments to module-level const objects (e.g., cache[key] = value).
• Use of global or globalThis.

Consider adding the no-restricted-syntax ESLint rule or a custom plugin to catch these patterns during development.

Related resources

• Shared responsibility model — Tenant safety
• Security for Forge apps — Data isolation
• Forge Storage
• Forge platform quotas and limits
• Logging guidelines for Forge app developers