Allow a list of servers to be passed in to the client

README.md

@@ -14,6 +14,8 @@ Simple python api for the chronos job scheduler
 ```
 import chronos
 c = chronos.connect("chronos.mesos.server.com:8080")
+# or specify multilple servers that will be tried in order
+c = chronos.connect(["chronos1.mesos.server.com:8080", "chronos2.mesos.server.com:8080"])
 
 # get list of scheduled jobs and their status as
 # [{ 'name': 'job1', ..}, { 'name': 'job2', ..}]

chronos/__init__.py

@@ -28,12 +28,21 @@
 from urllib import quote
 
 
+class ChronosAPIError(Exception):
+    pass
+
+
+class MissingFieldError(Exception):
+    pass
+
+
 class ChronosClient(object):
     _user = None
     _password = None
 
-    def __init__(self, hostname, proto="http", username=None, password=None, level='WARN'):
-        self.baseurl = "%s://%s" % (proto, hostname)
+    def __init__(self, servers, proto="http", username=None, password=None, level='WARN'):
+        server_list = servers if isinstance(servers, list) else [servers]
+        self.servers = ["%s://%s" % (proto, server) for server in server_list]
         if username and password:
             self._user = username
             self._password = password
@@ -86,9 +95,21 @@ def _call(self, url, method="GET", body=None, headers={}):
         conn = httplib2.Http(disable_ssl_certificate_validation=True)
         if self._user and self._password:
             conn.add_credentials(self._user, self._password)
-        endpoint = "%s%s" % (self.baseurl, quote(url))
-        self.logger.debug(endpoint)
-        return self._check(*conn.request(endpoint, method, body=body, headers=hdrs))
+
+        response = None
+        servers = list(self.servers)
+        while servers:
+            server = servers.pop(0)
+            endpoint = "%s%s" % (server, quote(url))
+            self.logger.debug(endpoint)
+            try:
+                response = self._check(*conn.request(endpoint, method, body=body, headers=hdrs))
+                self.logger.info('Got response from %s', endpoint)
+                return response
+            except Exception as e:
+                self.logger.error('Error while calling %s: %s', endpoint, e.message)
+
+        raise ChronosAPIError('No remaining Chronos servers to try')
 
     def _check(self, resp, content):
         status = resp.status
@@ -102,18 +123,18 @@ def _check(self, resp, content):
                 payload = content
 
         if payload is None and status != 204:
-            raise Exception("HTTP Error %d occurred." % status)
+            raise ChronosAPIError("Request to Chronos API failed: status: %d, response: %s" % (status, content))
 
         return payload
 
     def _check_fields(self, job):
         for k in ChronosJob.fields:
             if k not in job:
-                raise Exception("missing required field %s" % k)
+                raise MissingFieldError("missing required field %s" % k)
         for k in ChronosJob.one_of:
             if k in job:
                 return True
-        raise Exception("Job must include one of %s" % ChronosJob.one_of)
+        raise MissingFieldError("Job must include one of %s" % ChronosJob.one_of)
 
 
 class ChronosJob(object):
@@ -128,5 +149,5 @@ class ChronosJob(object):
     one_of = ["schedule", "parents"]
 
 
-def connect(hostname, proto="http", username=None, password=None):
-    return ChronosClient(hostname, proto="http", username=username, password=password)
+def connect(servers, proto="http", username=None, password=None):
+    return ChronosClient(servers, proto=proto, username=username, password=password)

itests/itest_utils.py

@@ -2,8 +2,6 @@
 from functools import wraps
 import os
 import signal
-import sys
-import threading
 import time
 
 import requests

tests/test_chronos_init.py

@@ -1,12 +1,28 @@
 import json
-
 import mock
+import pytest
+import httplib2
 
 import chronos
 
 
+def test_connect_accepts_single_host():
+    client = chronos.ChronosClient("localhost", proto="http")
+    assert client.servers == ['http://localhost']
+
+
+def test_connect_accepts_list_of_hosts():
+    client = chronos.ChronosClient(["host1", "host2"], proto="http")
+    assert client.servers == ['http://host1', 'http://host2']
+
+
+def test_connect_accepts_proto():
+    client = chronos.ChronosClient("localhost", proto="fake_proto")
+    assert client.servers == ['fake_proto://localhost']
+
+
 def test_check_accepts_json():
-    client = chronos.ChronosClient(hostname="localhost")
+    client = chronos.ChronosClient("localhost")
     fake_response = mock.Mock()
     fake_response.status = 200
     fake_content = '{ "foo": "bar" }'
@@ -15,9 +31,45 @@ def test_check_accepts_json():
 
 
 def test_check_returns_raw_response_when_not_json():
-    client = chronos.ChronosClient(hostname="localhost")
+    client = chronos.ChronosClient("localhost")
     fake_response = mock.Mock()
     fake_response.status = 401
     fake_content = 'UNAUTHORIZED'
     actual = client._check(fake_response, fake_content)
     assert actual == fake_content
+
+
+def test_uses_server_list():
+    client = chronos.ChronosClient(["host1", "host2", "host3"], proto="http")
+    good_request = (mock.Mock(status=204), '')
+    bad_request = (mock.Mock(status=500), '')
+
+    conn_mock = mock.Mock(request=mock.Mock(side_effect=[bad_request, good_request, bad_request]))
+    with mock.patch('httplib2.Http', return_value=conn_mock):
+        client._call('/fake_url')
+        assert conn_mock.request.call_count == 2
+
+
+def test_api_error_throws_exception():
+    client = chronos.ChronosClient(servers="localhost")
+    mock_response = mock.Mock()
+    mock_response.status = 500
+    mock_request = mock.Mock(return_value=(mock_response, None))
+    with mock.patch.object(httplib2.Http, 'request', mock_request):
+        with pytest.raises(chronos.ChronosAPIError):
+            client.list()
+
+
+def test_check_missing_fields():
+    client = chronos.ChronosClient(servers="localhost")
+    for field in chronos.ChronosJob.fields:
+        without_field = {x: 'foo' for x in filter(lambda y: y != field, chronos.ChronosJob.fields)}
+        with pytest.raises(chronos.MissingFieldError):
+            client._check_fields(without_field)
+
+
+def test_check_one_of():
+    client = chronos.ChronosClient(servers="localhost")
+    job = {field: 'foo' for field in chronos.ChronosJob.fields}
+    with pytest.raises(chronos.MissingFieldError):
+        client._check_fields(job)