diff --git a/tests/base.py b/tests/base.py
index e44cc11..e83994c 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -483,8 +483,8 @@
         self.__dict__.update(kw)
 
     def __repr__(self):
-        return ("<Completed build, result: %s name: %s #%s changes: %s>" %
-                (self.result, self.name, self.number, self.changes))
+        return ("<Completed build, result: %s name: %s uuid: %s changes: %s>" %
+                (self.result, self.name, self.uuid, self.changes))
 
 
 class FakeURLOpener(object):
@@ -541,12 +541,12 @@
 class FakeBuild(object):
     log = logging.getLogger("zuul.test")
 
-    def __init__(self, launch_server, job, number, node):
+    def __init__(self, launch_server, job, node):
         self.daemon = True
         self.launch_server = launch_server
         self.job = job
         self.jobdir = None
-        self.number = number
+        self.uuid = job.unique
         self.node = node
         self.parameters = json.loads(job.arguments)
         self.unique = self.parameters['ZUUL_UUID']
@@ -591,26 +591,8 @@
         self.wait_condition.release()
 
     def run(self):
-        data = {
-            'url': 'https://server/job/%s/%s/' % (self.name, self.number),
-            'name': self.name,
-            'number': self.number,
-            'manager': self.launch_server.worker.worker_id,
-            'worker_name': 'My Worker',
-            'worker_hostname': 'localhost',
-            'worker_ips': ['127.0.0.1', '192.168.1.1'],
-            'worker_fqdn': 'zuul.example.org',
-            'worker_program': 'FakeBuilder',
-            'worker_version': 'v1.1',
-            'worker_extra': {'something': 'else'}
-        }
-
         self.log.debug('Running build %s' % self.unique)
 
-        self.job.sendWorkData(json.dumps(data))
-        self.log.debug('Sent WorkData packet with %s' % json.dumps(data))
-        self.job.sendWorkStatus(0, 100)
-
         if self.launch_server.hold_jobs_in_build:
             self.log.debug('Holding build %s' % self.unique)
             self._wait()
@@ -680,8 +662,6 @@
         self.lock = threading.Lock()
         self.running_builds = []
         self.build_history = []
-        self._build_counter_lock = threading.Lock()
-        self.build_counter = 0
         self.fail_tests = {}
         self.job_builds = {}
 
@@ -720,16 +700,23 @@
         self.log.debug("Done releasing builds %s (%s)" %
                        (regex, len(self.running_builds)))
 
-    def launch(self, job):
-        with self._build_counter_lock:
-            self.build_counter += 1
-            build_counter = self.build_counter
+    def launchJob(self, job):
         node = None
-        build = FakeBuild(self, job, build_counter, node)
+        build = FakeBuild(self, job, node)
         job.build = build
         self.running_builds.append(build)
         self.job_builds[job.unique] = build
-        super(RecordingLaunchServer, self).launch(job)
+        super(RecordingLaunchServer, self).launchJob(job)
+
+    def stopJob(self, job):
+        self.log.debug("handle stop")
+        parameters = json.loads(job.arguments)
+        uuid = parameters['uuid']
+        for build in self.running_builds:
+            if build.unique == uuid:
+                build.aborted = True
+                build.release()
+        super(RecordingLaunchServer, self).stopJob(job)
 
     def runAnsible(self, jobdir, job):
         build = self.job_builds[job.unique]
@@ -742,9 +729,9 @@
 
         self.lock.acquire()
         self.build_history.append(
-            BuildHistory(name=build.name, number=build.number,
-                         result=result, changes=build.changes, node=build.node,
-                         uuid=build.unique, parameters=build.parameters,
+            BuildHistory(name=build.name, result=result, changes=build.changes,
+                         node=build.node, uuid=build.unique,
+                         parameters=build.parameters,
                          pipeline=build.parameters['ZUUL_PIPELINE'])
         )
         self.running_builds.remove(build)
@@ -1358,7 +1345,7 @@
                 return False
             if server_job.waiting:
                 continue
-            if build.number is None:
+            if build.url is None:
                 self.log.debug("%s has not reported start" % build)
                 return False
             worker_build = self.launch_server.job_builds.get(server_job.unique)
diff --git a/zuul/launcher/client.py b/zuul/launcher/client.py
index 14773cb..cd6dcfd 100644
--- a/zuul/launcher/client.py
+++ b/zuul/launcher/client.py
@@ -390,6 +390,7 @@
         gearman_job = gear.Job('launcher:launch', json.dumps(params),
                                unique=uuid)
         build.__gearman_job = gearman_job
+        build.__gearman_manager = None
         self.builds[uuid] = build
 
         if pipeline.precedence == zuul.model.PRECEDENCE_NORMAL:
@@ -428,7 +429,8 @@
             self.log.debug("Build %s has no associated gearman job" % build)
             return
 
-        if build.number is not None:
+        # TODOv3(jeblair): make a nicer way of recording build start.
+        if build.url is not None:
             self.log.debug("Build %s has already started" % build)
             self.cancelRunningBuild(build)
             self.log.debug("Canceled running build %s" % build)
@@ -444,7 +446,7 @@
         time.sleep(1)
 
         self.log.debug("Still unable to find build %s to cancel" % build)
-        if build.number:
+        if build.url:
             self.log.debug("Build %s has just started" % build)
             self.log.debug("Canceled running build %s" % build)
             self.cancelRunningBuild(build)
@@ -473,7 +475,7 @@
             # internal dict after it's added to the report queue.
             del self.builds[job.unique]
         else:
-            if not job.name.startswith("stop:"):
+            if not job.name.startswith("launcher:stop:"):
                 self.log.error("Unable to find build %s" % job.unique)
 
     def onWorkStatus(self, job):
@@ -481,14 +483,14 @@
         self.log.debug("Build %s update %s" % (job, data))
         build = self.builds.get(job.unique)
         if build:
+            started = (build.url is not None)
             # Allow URL to be updated
-            build.url = data.get('url') or build.url
+            build.url = data.get('url', build.url)
             # Update information about worker
             build.worker.updateFromData(data)
 
-            if build.number is None:
+            if not started:
                 self.log.info("Build %s started" % job)
-                build.number = data.get('number')
                 build.__gearman_manager = data.get('manager')
                 self.sched.onBuildStarted(build)
         else:
@@ -518,10 +520,12 @@
         return False
 
     def cancelRunningBuild(self, build):
+        if not build.__gearman_manager:
+            self.log.error("Build %s has no manager while canceling" %
+                           (build,))
         stop_uuid = str(uuid4().hex)
-        data = dict(name=build.job.name,
-                    number=build.number)
-        stop_job = gear.Job("stop:%s" % build.__gearman_manager,
+        data = dict(uuid=build.__gearman_job.unique)
+        stop_job = gear.Job("launcher:stop:%s" % build.__gearman_manager,
                             json.dumps(data), unique=stop_uuid)
         self.meta_jobs[stop_uuid] = stop_job
         self.log.debug("Submitting stop job: %s", stop_job)
diff --git a/zuul/launcher/server.py b/zuul/launcher/server.py
index 45c42dd..2a988b0 100644
--- a/zuul/launcher/server.py
+++ b/zuul/launcher/server.py
@@ -17,6 +17,7 @@
 import logging
 import os
 import shutil
+import socket
 import subprocess
 import tempfile
 import threading
@@ -113,6 +114,9 @@
 
     def __init__(self, config, connections={}):
         self.config = config
+        # TODOv3(mordred): make the launcher name more unique --
+        # perhaps hostname+pid.
+        self.hostname = socket.gethostname()
         self.zuul_url = config.get('merger', 'zuul_url')
 
         if self.config.has_option('merger', 'git_dir'):
@@ -161,7 +165,7 @@
 
     def register(self):
         self.worker.registerFunction("launcher:launch")
-        # TODOv3: abort
+        self.worker.registerFunction("launcher:stop:%s" % self.hostname)
         self.worker.registerFunction("merger:merge")
         self.worker.registerFunction("merger:cat")
 
@@ -204,7 +208,10 @@
                 try:
                     if job.name == 'launcher:launch':
                         self.log.debug("Got launch job: %s" % job.unique)
-                        self.launch(job)
+                        self.launchJob(job)
+                    elif job.name.startswith('launcher:stop'):
+                        self.log.debug("Got stop job: %s" % job.unique)
+                        self.stopJob(job)
                     elif job.name == 'merger:cat':
                         self.log.debug("Got cat job: %s" % job.unique)
                         self.cat(job)
@@ -220,7 +227,7 @@
             except Exception:
                 self.log.exception("Exception while getting job")
 
-    def launch(self, job):
+    def launchJob(self, job):
         thread = threading.Thread(target=self._launch, args=(job,))
         thread.start()
 
@@ -243,18 +250,35 @@
 
             # TODOv3: Ansible the ansible thing here.
             self.prepareAnsibleFiles(jobdir, args)
-            result = self.runAnsible(jobdir, job)
 
             data = {
+                'manager': self.hostname,
                 'url': 'https://server/job',
-                'number': 1
             }
+
+            # TODOv3:
+            # 'name': self.name,
+            # 'manager': self.launch_server.hostname,
+            # 'worker_name': 'My Worker',
+            # 'worker_hostname': 'localhost',
+            # 'worker_ips': ['127.0.0.1', '192.168.1.1'],
+            # 'worker_fqdn': 'zuul.example.org',
+            # 'worker_program': 'FakeBuilder',
+            # 'worker_version': 'v1.1',
+            # 'worker_extra': {'something': 'else'}
+
             job.sendWorkData(json.dumps(data))
             job.sendWorkStatus(0, 100)
 
+            result = self.runAnsible(jobdir, job)
+
             result = dict(result=result)
             job.sendWorkComplete(json.dumps(result))
 
+    def stopJob(self, job):
+        # TODOv3: implement.
+        job.sendWorkComplete()
+
     def getHostList(self, args):
         # TODOv3: This should get the appropriate nodes from nodepool,
         # or in the unit tests, be overriden to return localhost.
diff --git a/zuul/model.py b/zuul/model.py
index f737d9e..ce3d1a2 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -487,7 +487,6 @@
         self.job = job
         self.uuid = uuid
         self.url = None
-        self.number = None
         self.result = None
         self.build_set = None
         self.launch_time = time.time()
@@ -975,7 +974,6 @@
                 'pipeline': build.pipeline.name if build else None,
                 'canceled': build.canceled if build else None,
                 'retry': build.retry if build else None,
-                'number': build.number if build else None,
                 'node_labels': build.node_labels if build else [],
                 'node_name': build.node_name if build else None,
                 'worker': worker,