feat(lambda): read cloud.account.id from symlink in Lambda detector (#507)

* feat(lambda): read cloud.account.id from /tmp/.otel-account-id symlink

The Lambda resource detector now reads the /tmp/.otel-account-id symlink
via readlink() and sets cloud.account.id on the resource. If the symlink
is missing or unreadable, detection proceeds without the attribute.

* Rename symlink to .otel-aws-account-id

Author: RaphaelManke

src/Aws/src/Lambda/Detector.php

@@ -37,6 +37,7 @@ class Detector implements ResourceDetectorInterface
     private const LAMBDA_VERSION_ENV = 'AWS_LAMBDA_FUNCTION_VERSION';
     private const AWS_REGION_ENV = 'AWS_REGION';
     private const CLOUD_PROVIDER = 'aws';
+    private const ACCOUNT_ID_SYMLINK_PATH = '/tmp/.otel-aws-account-id';
 
     public function getResource(): ResourceInfo
     {
@@ -51,13 +52,23 @@ public function getResource(): ResourceInfo
         $functionVersion = $functionVersion ? $functionVersion : null;
         $awsRegion = $awsRegion ? $awsRegion : null;
 
-        return !$lambdaName && !$awsRegion && !$functionVersion
+        $accountId = null;
+        $symlinkPath = self::ACCOUNT_ID_SYMLINK_PATH;
+        if (is_link($symlinkPath)) {
+            $target = readlink($symlinkPath);
+            if ($target !== false) {
+                $accountId = $target;
+            }
+        }
+
+        return !$lambdaName && !$awsRegion && !$functionVersion && !$accountId
             ? ResourceInfoFactory::emptyResource()
             : ResourceInfo::create(Attributes::create([
                 ResourceAttributes::FAAS_NAME => $lambdaName,
                 ResourceAttributes::FAAS_VERSION => $functionVersion,
                 ResourceAttributes::CLOUD_REGION => $awsRegion,
                 ResourceAttributes::CLOUD_PROVIDER => self::CLOUD_PROVIDER,
+                ResourceAttributes::CLOUD_ACCOUNT_ID => $accountId,
             ]));
     }
 }

src/Aws/tests/Unit/Lambda/DetectorTest.php

@@ -99,4 +99,71 @@ public function TestIncompleteLambda2()
         putenv(self::LAMBDA_NAME_ENV);
         putenv(self::AWS_REGION_ENV);
     }
+
+    private const ACCOUNT_ID_SYMLINK_PATH = '/tmp/.otel-aws-account-id';
+
+    private function removeSymlinkIfExists(): ?string
+    {
+        if (is_link(self::ACCOUNT_ID_SYMLINK_PATH)) {
+            $previous = readlink(self::ACCOUNT_ID_SYMLINK_PATH);
+            unlink(self::ACCOUNT_ID_SYMLINK_PATH);
+
+            return $previous !== false ? $previous : null;
+        }
+
+        return null;
+    }
+
+    /**
+     * @test
+     */
+    public function TestAccountIdFromSymlink()
+    {
+        $previous = $this->removeSymlinkIfExists();
+
+        $accountId = '123456789012';
+        symlink($accountId, self::ACCOUNT_ID_SYMLINK_PATH);
+
+        try {
+            putenv(self::LAMBDA_NAME_ENV . '=' . self::LAMBDA_NAME_VAL);
+
+            $detector = new Detector();
+            $resource = $detector->getResource();
+
+            $this->assertEquals(
+                $accountId,
+                $resource->getAttributes()->get(ResourceAttributes::CLOUD_ACCOUNT_ID)
+            );
+        } finally {
+            unlink(self::ACCOUNT_ID_SYMLINK_PATH);
+            if ($previous !== null) {
+                symlink($previous, self::ACCOUNT_ID_SYMLINK_PATH);
+            }
+            putenv(self::LAMBDA_NAME_ENV);
+        }
+    }
+
+    /**
+     * @test
+     */
+    public function TestMissingAccountIdSymlink()
+    {
+        $previous = $this->removeSymlinkIfExists();
+
+        try {
+            putenv(self::LAMBDA_NAME_ENV . '=' . self::LAMBDA_NAME_VAL);
+
+            $detector = new Detector();
+            $resource = $detector->getResource();
+
+            $this->assertNull(
+                $resource->getAttributes()->get(ResourceAttributes::CLOUD_ACCOUNT_ID)
+            );
+        } finally {
+            if ($previous !== null) {
+                symlink($previous, self::ACCOUNT_ID_SYMLINK_PATH);
+            }
+            putenv(self::LAMBDA_NAME_ENV);
+        }
+    }
 }