Try to auto-detect mailman-core's IP address.

Fixes #133

web/mailman-web/settings.py

@@ -27,6 +27,7 @@ https://docs.djangoproject.com/en/1.8/ref/settings/
 
 # Build paths inside the project like this: os.path.join(BASE_DIR, ...)
 import os
+import socket
 import dj_database_url
 
 BASE_DIR = os.path.dirname(os.path.abspath(__file__))
@@ -55,12 +56,15 @@ ALLOWED_HOSTS = [
     os.environ.get('DJANGO_ALLOWED_HOSTS'),
 ]
 
+# Try to get the address of Mailman Core automatically.
+MAILMAN_HOST_IP_AUTO = socket.gethostbyname('mailman-core')
+
 # Mailman API credentials
 MAILMAN_REST_API_URL = os.environ.get('MAILMAN_REST_URL', 'http://mailman-core:8001')
 MAILMAN_REST_API_USER = os.environ.get('MAILMAN_REST_USER', 'restadmin')
 MAILMAN_REST_API_PASS = os.environ.get('MAILMAN_REST_PASSWORD', 'restpass')
 MAILMAN_ARCHIVER_KEY = os.environ.get('HYPERKITTY_API_KEY')
-MAILMAN_ARCHIVER_FROM = ('mailman-core', os.environ.get('MAILMAN_HOST_IP', '172.19.199.2'))
+MAILMAN_ARCHIVER_FROM = (MAILMAN_HOST_IP_AUTO, os.environ.get('MAILMAN_HOST_IP', '172.19.199.2'))
 
 # Application definition
 
@@ -190,7 +194,6 @@ USE_L10N = True
 
 USE_TZ = True
 
-
 STATIC_ROOT = '/opt/mailman-web-data/static'
 
 STATIC_URL = '/static/'