Automatically configure all interfaces (including virtual!) at boot

On EC2-VPC we have the ability to attach multiple addresses to one
interface, and multiple interfaces to one machine.

We should configure those interfaces whenever our system boots, and
ideally whenever networking is restarted.

This commit adds a script that is executed once eth0 is brought up that
proceeds to configure all subsequent interfaces, real and virtual.

The script is configured to be installed (along with the helper script
that calls it) on all systems via Puppet.

(imported from commit fdc153ef649edbb8fedd40ff4d77262aae593c39)

servers/puppet/modules/humbug/files/zulip-ec2-configure-interfaces

@@ -0,0 +1,71 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+'''Configure a host for EC2-VPC dynamically assigned network interfaces
+
+Amazon VPC gives us a good deal of flexibility compared to classic EC2.
+However there are limitations; you can assign multiple IPs to a host
+yet only the first IP per interface will be DHCP assigned, and you are
+limited in the total number of interfaces you have, so doing one-IP-per-
+interface is also untenable.
+
+This script grabs the metadata provided by AWS and uses it to correctly
+configure all available network interfaces.
+
+It is suitable to be hooked in to system boot and network
+reconfiguration scripts.
+
+Note that it currently does not handle the deconfiguration of
+interfaces.
+
+'''
+
+import sys
+import syslog
+import subprocess
+import re
+
+import boto.utils
+import netifaces
+
+def address_of(device_id):
+    try:
+        return netifaces.ifaddresses("eth%i" % device_id)[netifaces.AF_INET][0]['addr']
+    except KeyError:
+        return None
+
+syslog.openlog(logoption=syslog.LOG_PID)
+syslog.syslog("ec2ify starting")
+
+macs = boto.utils.get_instance_metadata()["network"]["interfaces"]["macs"]
+ids = [int(macdata['device-number']) for macdata in macs.values()]
+ifaces = [iface for iface in netifaces.interfaces() if ":" not in iface and iface != "lo"]
+
+# Number of IDs should equal number of interfaces
+if len(ids) != len(ifaces):
+    syslog.syslog(syslog.LOG_ERR, "Metadata indicated %i interfaces but we have %i!" % (len(ids), len(ifaces)))
+    sys.exit(1)
+
+for device in macs.values():
+    # There's an annoying API inconsistency here:
+    #   If you have multiple IPs, local-ipv4s is a list.
+    #   If you only have one, local-ipv4s is a string.
+    # Who knew?
+    if type(device['local-ipv4s']) is str:
+        # Only do dhcp, don't try to assign addresses
+        to_configure = [device['local-ipv4s']]
+    else:
+        to_configure = list(device['local-ipv4s'])
+    device_number = int(device['device-number'])
+
+    if address_of(device_number) is None:
+        # If the device was not autoconfigured, do so now.
+        syslog.syslog(syslog.LOG_INFO, "Device eth%i not configured, starting dhcpd" % device_number)
+        subprocess.check_call(['/sbin/dhcpcd', 'eth%i' % device_number])
+
+    to_configure.remove(address_of(device_number))
+
+    for (count, ip) in enumerate(to_configure):
+        # Configure the IP via a virtual interface
+        device = "eth%i:%i" % (device_number, count)
+        syslog.syslog(syslog.LOG_INFO, "Configuring %s with IP %s" % (device, ip))
+        subprocess.check_call(['/sbin/ifconfig', device, ip])

servers/puppet/modules/humbug/files/zulip-ec2-configure-interfaces_if-up.d.sh

@@ -0,0 +1,13 @@
+#! /bin/sh
+# Run zulip-ec2-configure-interfaces when eth0 is brought up
+
+set -e
+
+# Only run from ifup.
+if [ "$MODE" != start ]; then
+	exit 0
+fi
+
+if [ "$IFACE" = eth0 ]; then
+	/usr/local/sbin/zulip-ec2-configure-interfaces
+fi

servers/puppet/modules/humbug/manifests/base.pp

@@ -4,7 +4,8 @@ class humbug::base {
                 "openssh-server", "python-pip", "puppet-el",
                 "iptables-persistent", "nagios-plugins-basic", "munin-node",
                 "munin-plugins-extra", "postgresql-client-9.1",
-		"debian-goodies", "moreutils", "python-requests", ]
+		"debian-goodies", "moreutils", "python-requests", "ipython",
+                "python-boto", "python-netifaces" ]
   package { $packages: ensure => "installed" }
 
 
@@ -73,6 +74,18 @@ class humbug::base {
     source     => 'puppet:///modules/humbug/apt/apt.conf.d/02periodic',
   }
 
+  file { '/usr/local/sbin/zulip-ec2-configure-interfaces':
+    ensure     => file,
+    mode       => 755,
+    source     => 'puppet:///modules/humbug/zulip-ec2-configure-interfaces',
+  }
+
+  file { '/etc/network/if-up.d/zulip-ec2-configure-interfaces_if-up.d.sh':
+    ensure     => file,
+    mode       => 755,
+    source     => 'puppet:///modules/humbug/zulip-ec2-configure-interfaces_if-up.d.sh',
+  }
+
   file { '/etc/ssh/sshd_config':
     require    => Package['openssh-server'],
     ensure     => file,
@@ -81,6 +94,7 @@ class humbug::base {
     group      => 'root',
     mode       => 644,
   }
+
   service { 'ssh':
     ensure     => running,
     subscribe  => File['/etc/ssh/sshd_config'],