Only listen on a port starting from 9009

Partially reverts #21818. Fixes #24722.

NEWS.md

@@ -259,7 +259,8 @@ This section lists changes that do not have deprecation warnings.
     rather than from environment variables ([#19636]).
 
   * Workers now listen on an ephemeral port assigned by the OS. Previously workers would
-    listen on the first free port available from 9009 ([#21818]).
+    listen on the first free port available from 9009 ([#21818]). Version 0.6.1 only.
+    Reverted in 0.6.2
 
 
 Library improvements

base/distributed/cluster.jl

@@ -153,7 +153,7 @@ function start_worker(out::IO, cookie::AbstractString)
     init_worker(cookie)
     interface = IPv4(LPROC.bind_addr)
     if LPROC.bind_port == 0
-        (port, sock) = listenany(interface, UInt16(0))
+        (port, sock) = listenany(interface, UInt16(9009))
         LPROC.bind_port = port
     else
         sock = listen(interface, LPROC.bind_port)

doc/src/manual/parallel-computing.md

@@ -1231,8 +1231,8 @@ as local laptops, departmental clusters, or even the cloud. This section covers
 requirements for the inbuilt `LocalManager` and `SSHManager`:
 
   * The master process does not listen on any port. It only connects out to the workers.
-  * Each worker binds to only one of the local interfaces and listens on an ephemeral port number
-    assigned by the OS.
+  * Each worker binds to only one of the local interfaces and listens on the first free port starting
+    from `9009`.
   * `LocalManager`, used by `addprocs(N)`, by default binds only to the loopback interface. This means
     that workers started later on remote hosts (or by anyone with malicious intentions) are unable
     to connect to the cluster. An `addprocs(4)` followed by an `addprocs(["remote_host"])` will fail.
@@ -1250,9 +1250,8 @@ requirements for the inbuilt `LocalManager` and `SSHManager`:
     authenticated via public key infrastructure (PKI). Authentication credentials can be supplied
     via `sshflags`, for example ```sshflags=`-e <keyfile>` ```.
 
-    In an all-to-all topology (the default), all workers connect to each other via plain TCP sockets.
-    The security policy on the cluster nodes must thus ensure free connectivity between workers for
-    the ephemeral port range (varies by OS).
+    Note that worker-worker connections are still plain TCP and the local security policy on the remote
+    cluster must allow for free connections between worker nodes, at least for ports 9009 and above.
 
     Securing and encrypting all worker-worker traffic (via SSH) or encrypting individual messages
     can be done via a custom ClusterManager.