cluster: overriding inspector port

doc/api/cluster.md

@@ -700,18 +700,21 @@ changes:
 -->
 
 * {Object}
-  * `execArgv` {Array} list of string arguments passed to the Node.js
+  * `execArgv` {Array} List of string arguments passed to the Node.js
     executable. (Default=`process.execArgv`)
-  * `exec` {string} file path to worker file.  (Default=`process.argv[1]`)
-  * `args` {Array} string arguments passed to worker.
+  * `exec` {string} File path to worker file.  (Default=`process.argv[1]`)
+  * `args` {Array} String arguments passed to worker.
     (Default=`process.argv.slice(2)`)
-  * `silent` {boolean} whether or not to send output to parent's stdio.
+  * `silent` {boolean} Whether or not to send output to parent's stdio.
     (Default=`false`)
   * `stdio` {Array} Configures the stdio of forked processes. Because the
     cluster module relies on IPC to function, this configuration must contain an
     `'ipc'` entry. When this option is provided, it overrides `silent`.
   * `uid` {number} Sets the user identity of the process. (See setuid(2).)
   * `gid` {number} Sets the group identity of the process. (See setgid(2).)
+  * `inspectPort` {number|function} Sets inspector port of worker.
+  Accepts number, or function that evaluates to number. By default
+  each worker gets port, incremented from master's `process.debugPort`.
 
 After calling `.setupMaster()` (or `.fork()`) this settings object will contain
 the settings, including the default values.
@@ -727,26 +730,19 @@ changes:
     description: The `stdio` option is supported now.
 -->
 
-* `settings` {Object}
-  * `exec` {string} file path to worker file.  (Default=`process.argv[1]`)
-  * `args` {Array} string arguments passed to worker.
-    (Default=`process.argv.slice(2)`)
-  * `silent` {boolean} whether or not to send output to parent's stdio.
-    (Default=`false`)
-  * `stdio` {Array} Configures the stdio of forked processes. When this option
-    is provided, it overrides `silent`.
+* `settings` {Object} see [`cluster.settings`][]
 
 `setupMaster` is used to change the default 'fork' behavior. Once called,
 the settings will be present in `cluster.settings`.
 
 Note that:
 
-* any settings changes only affect future calls to `.fork()` and have no
-  effect on workers that are already running
+* Any settings changes only affect future calls to `.fork()` and have no
+  effect on workers that are already running.
 * The *only* attribute of a worker that cannot be set via `.setupMaster()` is
-  the `env` passed to `.fork()`
-* the defaults above apply to the first call only, the defaults for later
-  calls is the current value at the time of `cluster.setupMaster()` is called
+  the `env` passed to `.fork()`.
+* The defaults above apply to the first call only, the defaults for later
+  calls is the current value at the time of `cluster.setupMaster()` is called.
 
 Example:
 
@@ -834,3 +830,4 @@ socket.on('data', (id) => {
 [Child Process module]: child_process.html#child_process_child_process_fork_modulepath_args_options
 [child_process event: 'exit']: child_process.html#child_process_event_exit
 [child_process event: 'message']: child_process.html#child_process_event_message
+[`cluster.settings`]: #clustersettings

lib/internal/cluster/master.js

@@ -12,6 +12,7 @@ const cluster = new EventEmitter();
 const intercom = new EventEmitter();
 const SCHED_NONE = 1;
 const SCHED_RR = 2;
+const {isLegalPort} = require('internal/net');
 
 module.exports = cluster;
 
@@ -104,8 +105,23 @@ function createWorkerProcess(id, env) {
   workerEnv.NODE_UNIQUE_ID = '' + id;
 
   if (execArgv.some((arg) => arg.match(debugArgRegex))) {
-    execArgv.push(`--inspect-port=${process.debugPort + debugPortOffset}`);
-    debugPortOffset++;
+    let inspectPort;
+    if ('inspectPort' in cluster.settings) {
+      if (typeof cluster.settings.inspectPort === 'function')
+        inspectPort = cluster.settings.inspectPort();
+      else
+        inspectPort = cluster.settings.inspectPort;
+
+      if (!isLegalPort(inspectPort)) {
+        throw new TypeError('cluster.settings.inspectPort' +
+          ' is invalid');
+      }
+    } else {
+      inspectPort = process.debugPort + debugPortOffset;
+      debugPortOffset++;
+    }
+
+    execArgv.push(`--inspect-port=${inspectPort}`);
   }
 
   return fork(cluster.settings.exec, cluster.settings.args, {