Add an option to use AWS instance address in a PostgreSQL connection string.

When PostgreSQL is running inside the docker container, it should provide
the address of the host it's running on and not the address from inside
of the container to the outside world.

governor.py

@@ -7,6 +7,7 @@ from helpers.etcd import Etcd
 from helpers.postgresql import Postgresql
 from helpers.ha import Ha
 
+INSTANCE_METADATA_URL = "http://169.254.169.254/latest/meta-data/"
 
 logging.basicConfig(format='%(asctime)s %(levelname)s: %(message)s', level=logging.INFO)
 
@@ -14,8 +15,19 @@ f = open(sys.argv[1], "r")
 config = yaml.load(f.read())
 f.close()
 
+if config.get('aws_use_host_address', False):
+    # get host address of the AWS host via a call to
+    # http://169.254.169.254/latest/meta-data/local-ipv4
+    try:
+        aws_host_address = urllib2.urlopen(INSTANCE_METADATA_URL+"/local-ipv4").read()
+    except (urllib2.HTTPError, urllib2.URLError) as e:
+        logging.error("Error retrieiving IPv4 address from AWS instance: {0}".format(e))
+        aws_host_address = None
+else:
+    aws_host_address = None
+
 etcd = Etcd(config["etcd"])
-postgresql = Postgresql(config["postgresql"])
+postgresql = Postgresql(config["postgresql"], aws_host_address)
 ha = Ha(postgresql, etcd)
 
 # stop postgresql on script exit

helpers/postgresql.py

@@ -9,7 +9,7 @@ logger = logging.getLogger(__name__)
 
 class Postgresql:
 
-    def __init__(self, config):
+    def __init__(self, config, aws_host_address=None):
         self.name = config["name"]
         self.host, self.port = config["listen"].split(":")
         self.data_dir = config["data_dir"]
@@ -18,7 +18,8 @@ class Postgresql:
         self.config = config
 
         self.cursor_holder = None
-        self.connection_string = "postgres://%s:%s@%s:%s/postgres" % (self.replication["username"], self.replication["password"], self.host, self.port)
+        connection_host = aws_host_address or self.host
+        self.connection_string = "postgres://%s:%s@%s:%s/postgres" % (self.replication["username"], self.replication["password"], connection_host, self.port)
 
         self.conn = None
 

postgres0.yml

@@ -1,4 +1,5 @@
 loop_wait: 10
+aws_use_host_address: "on"
 etcd:
   scope: batman
   ttl: 30

postgres1.yml

@@ -1,4 +1,5 @@
 loop_wait: 10
+aws_use_host_address: "on"
 etcd:
   scope: batman
   ttl: 30