fix(cli): large context causes E2BIG error during synthesis on Linux (a…

…ws#21230)

Instead of passing the context in an environment variable, the CLI now writes the context to a temporary file and sets an environment variable only with the location. The app then uses that location to read from the file.

Also tested manually on a Linux machine.

Fixes aws#19261.

### All Submissions:

* [x] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/core/lib/app.ts

@@ -1,5 +1,6 @@
 import * as cxapi from '@aws-cdk/cx-api';
 import { Construct } from 'constructs';
+import * as fs from 'fs-extra';
 import { addCustomSynthesis, ICustomSynthesis } from './private/synthesis';
 import { TreeMetadata } from './private/tree-metadata';
 import { Stage } from './stage';
@@ -142,16 +143,23 @@ export class App extends Stage {
       this.node.setContext(k, v);
     }
 
-    // read from environment
-    const contextJson = process.env[cxapi.CONTEXT_ENV];
-    const contextFromEnvironment = contextJson
-      ? JSON.parse(contextJson)
-      : { };
 
-    for (const [k, v] of Object.entries(contextFromEnvironment)) {
+    const context = this.readContextFromTempFile() ?? this.readContextFromEnvironment() ?? {};
+    for (const [k, v] of Object.entries(context)) {
       this.node.setContext(k, v);
     }
   }
+
+  private readContextFromTempFile() {
+    const location = process.env[cxapi.CONTEXT_LOCATION_ENV];
+    return location != null ? fs.readJSONSync(location) : undefined;
+  }
+
+  // for backward compatibility with old versions of the CLI
+  private readContextFromEnvironment() {
+    const contextJson = process.env[cxapi.CONTEXT_ENV];
+    return contextJson ? JSON.parse(contextJson) : undefined;
+  }
 }
 
 /**

packages/@aws-cdk/core/test/app.test.ts

@@ -1,6 +1,9 @@
+import * as os from 'os';
+import * as path from 'path';
 import { ContextProvider } from '@aws-cdk/cloud-assembly-schema';
 import * as cxapi from '@aws-cdk/cx-api';
 import { Construct } from 'constructs';
+import * as fs from 'fs-extra';
 import { CfnResource, DefaultStackSynthesizer, Stack, StackProps } from '../lib';
 import { Annotations } from '../lib/annotations';
 import { App, AppProps } from '../lib/app';
@@ -101,25 +104,49 @@ describe('app', () => {
     });
   });
 
-  test('context can be passed through CDK_CONTEXT', () => {
-    process.env[cxapi.CONTEXT_ENV] = JSON.stringify({
+  test('context can be passed through CDK_CONTEXT_LOCATION', async () => {
+    const contextDir = await fs.mkdtemp(path.join(os.tmpdir(), 'cdk-context'));
+    const contextLocation = path.join(contextDir, 'context-temp.json');
+    fs.writeJSONSync(contextLocation, {
       key1: 'val1',
       key2: 'val2',
     });
+    process.env[cxapi.CONTEXT_LOCATION_ENV] = contextLocation;
+
     const prog = new App();
     expect(prog.node.tryGetContext('key1')).toEqual('val1');
     expect(prog.node.tryGetContext('key2')).toEqual('val2');
   });
 
-  test('context passed through CDK_CONTEXT has precedence', () => {
+  test('context can be passed through CDK_CONTEXT', async () => {
     process.env[cxapi.CONTEXT_ENV] = JSON.stringify({
       key1: 'val1',
       key2: 'val2',
     });
+
+    const prog = new App();
+    expect(prog.node.tryGetContext('key1')).toEqual('val1');
+    expect(prog.node.tryGetContext('key2')).toEqual('val2');
+  });
+
+  test('context passed through CDK_CONTEXT_LOCATION has precedence', async () => {
+    const contextDir = await fs.mkdtemp(path.join(os.tmpdir(), 'cdk-context'));
+    const contextLocation = path.join(contextDir, 'context-temp.json');
+    fs.writeJSONSync(contextLocation, {
+      key1: 'val1',
+      key2: 'val2',
+    });
+    process.env[cxapi.CONTEXT_LOCATION_ENV] = contextLocation;
+
+    process.env[cxapi.CONTEXT_ENV] = JSON.stringify({
+      key1: 'val3',
+      key2: 'val4',
+    });
+
     const prog = new App({
       context: {
-        key1: 'val3',
-        key2: 'val4',
+        key1: 'val5',
+        key2: 'val6',
       },
     });
     expect(prog.node.tryGetContext('key1')).toEqual('val1');

packages/@aws-cdk/cx-api/lib/cxapi.ts

@@ -4,6 +4,11 @@
 export const OUTDIR_ENV = 'CDK_OUTDIR';
 export const CONTEXT_ENV = 'CDK_CONTEXT_JSON';
 
+/**
+ * The name of the temporary file where the context is stored.
+ */
+export const CONTEXT_LOCATION_ENV = 'CDK_CONTEXT_LOCATION';
+
 /**
  * Environment variable set by the CDK CLI with the default AWS account ID.
  */

packages/aws-cdk/lib/api/cxapp/exec.ts

@@ -1,4 +1,5 @@
 import * as childProcess from 'child_process';
+import * as os from 'os';
 import * as path from 'path';
 import * as cxschema from '@aws-cdk/cloud-assembly-schema';
 import * as cxapi from '@aws-cdk/cx-api';
@@ -44,7 +45,11 @@ export async function execProgram(aws: SdkProvider, config: Configuration): Prom
   context[cxapi.BUNDLING_STACKS] = bundlingStacks;
 
   debug('context:', context);
-  env[cxapi.CONTEXT_ENV] = JSON.stringify(context);
+
+  const contextDir = await fs.mkdtemp(path.join(os.tmpdir(), 'cdk-context'));
+  const contextLocation = path.join(contextDir, 'context-temp.json');
+  fs.writeJSONSync(contextLocation, context);
+  env[cxapi.CONTEXT_LOCATION_ENV] = contextLocation;
 
   const build = config.settings.get(['build']);
   if (build) {
@@ -85,7 +90,11 @@ export async function execProgram(aws: SdkProvider, config: Configuration): Prom
 
   await exec(commandLine.join(' '));
 
-  return createAssembly(outdir);
+  const assembly = createAssembly(outdir);
+
+  fs.removeSync(path.dirname(contextLocation));
+
+  return assembly;
 
   function createAssembly(appDir: string) {
     try {

packages/aws-cdk/lib/commands/doctor.ts

@@ -51,7 +51,7 @@ function displayCdkEnvironmentVariables() {
   print('ℹ️ CDK environment variables:');
   let healthy = true;
   for (const key of keys.sort()) {
-    if (key === cxapi.CONTEXT_ENV || key === cxapi.OUTDIR_ENV) {
+    if (key === cxapi.CONTEXT_ENV || key === cxapi.CONTEXT_LOCATION_ENV || key === cxapi.OUTDIR_ENV) {
       print(`  - ${chalk.red(key)} = ${chalk.green(process.env[key]!)} (⚠️ reserved for use by the CDK toolkit)`);
       healthy = false;
     } else {