OpenStack might not do everything you need it to do out of the box. To add a new feature, you can follow different paths. customization paths available To take the first path, you can modify the OpenStack code directly. Learn how to contribute, follow the code review workflow, make your changes, and contribute them back to the upstream OpenStack project. This path is recommended if the feature you need requires deep integration with an existing project. The community is always open to contributions and welcomes new functionality that follows the feature-development guidelines. This path still requires you to use DevStack for testing your feature additions, so this chapter walks you through the DevStack environment. OpenStack community customization and For the second path, you can write new features and plug them in using changes to a configuration file. If the project where your feature would need to reside uses the Python Paste framework, you can create middleware for it and plug it in through configuration. There may also be specific ways of customizing a project, such as creating a new scheduler driver for Compute or a custom tab for the dashboard. This chapter focuses on the second path for customizing OpenStack by providing two examples for writing new features. The first example shows how to modify Object Storage (swift) middleware to add a new feature, and the second example provides a new scheduler feature for OpenStack Compute (nova). To customize OpenStack this way you need a development environment. The best way to get an environment up and running quickly is to run DevStack within your cloud.

To create a development environment, you can use DevStack. DevStack is essentially a collection of shell scripts and configuration files that builds an OpenStack development environment for you. You use it to create such an environment for developing a new feature. customization development environment creation for development environments, creating DevStack development environment creation You can find all of the documentation at the DevStack website. Boot an instance from the dashboard or the nova command-line interface (CLI) with the following parameters: Name: devstack-havana Image: Ubuntu 12.04 LTS Memory Size: 4 GB RAM Disk Size: minimum 5 GB If you are using the nova client, specify --flavor 3 for the nova boot command to get adequate memory and disk sizes. Log in and set up DevStack. Here's an example of the commands you can use to set up DevStack on a virtual machine: Log in to the instance: $ ssh username@my.instance.ip.address Update the virtual machine's operating system: # apt-get -y update Install git: # apt-get -y install git Clone the stable/havana branch of the devstack repository: $ git clone https://github.com/openstack-dev/devstack.git -b stable/havana devstack/ Change to the devstack repository: $ cd devstack (Optional) If you've logged in to your instance as the root user, you must create a "stack" user; otherwise you'll run into permission issues. If you've logged in as a user other than root, you can skip these steps: Run the DevStack script to create the stack user: # tools/create-stack-user.sh Give ownership of the devstack directory to the stack user: # chown -R stack:stack /root/devstack Set some permissions you can use to view the DevStack screen later: # chmod o+rwx /dev/pts/0 Switch to the stack user: $ su stack Edit the localrc configuration file that controls what DevStack will deploy. Copy the example localrc file at the end of this section (): $ vim localrc Run the stack script that will install OpenStack: $ ./stack.sh When the stack script is done, you can open the screen session it started to view all of the running OpenStack services: $ screen -r stack Press Ctrl A followed by 0 to go to the first screen window. The stack.sh script takes a while to run. Perhaps you can take this opportunity to join the OpenStack Foundation. Screen is a useful program for viewing many related services at once. For more information, see the GNU screen quick reference. Now that you have an OpenStack development environment, you're free to hack around without worrying about damaging your production deployment. provides a working environment for running OpenStack Identity, Compute, Block Storage, Image service, the OpenStack dashboard, and Object Storage with the stable/havana branches as the starting point. # Credentials ADMIN_PASSWORD=devstack MYSQL_PASSWORD=devstack RABBIT_PASSWORD=devstack SERVICE_PASSWORD=devstack SERVICE_TOKEN=devstack # OpenStack Identity Service branch KEYSTONE_BRANCH=stable/havana # OpenStack Compute branch NOVA_BRANCH=stable/havana # OpenStack Block Storage branch CINDER_BRANCH=stable/havana # OpenStack Image service branch GLANCE_BRANCH=stable/havana # OpenStack Dashboard branch HORIZON_BRANCH=stable/havana # OpenStack Object Storage branch SWIFT_BRANCH=stable/havana enable_service swift # Object Storage Settings SWIFT_HASH=66a3d6b56c1f479c8b4e70ab5c2000f5 SWIFT_REPLICAS=1 # Block Storage Setting VOLUME_BACKING_FILE_SIZE=20480M # Output LOGFILE=/opt/stack/logs/stack.sh.log VERBOSE=True LOG_COLOR=False SCREEN_LOGDIR=/opt/stack/logs

OpenStack Object Storage, known as swift when reading the code, is based on the Python Paste framework. The best introduction to its architecture is A Do-It-Yourself Framework. Because of the swift project's use of this framework, you are able to add features to a project by placing some custom code in a project's pipeline without having to change any of the core code. Paste framework Python swift swift middleware Object Storage customization of customization Object Storage DevStack customizing Object Storage (swift) Imagine a scenario where you have public access to one of your containers, but what you really want is to restrict access to that to a set of IPs based on a whitelist. In this example, we'll create a piece of middleware for swift that allows access to a container from only a set of IP addresses, as determined by the container's metadata items. Only those IP addresses that you explicitly whitelist using the container's metadata will be able to access the container. This example is for illustrative purposes only. It should not be used as a container IP whitelist solution without further development and extensive security testing. security issues middleware example When you join the screen session that stack.sh starts with screen -r stack, you see a screen for each service running, which can be a few or several, depending on how many services you configured DevStack to run. The asterisk * indicates which screen window you are viewing. This example shows we are viewing the key (for keystone) screen window: 0$ shell 1$ key* 2$ horizon 3$ s-proxy 4$ s-object 5$ s-container 6$ s-account The purpose of the screen windows are as follows: shell A shell where you can get some work done key* The keystone service horizon The horizon dashboard web application s-{name} The swift services All of the code for OpenStack lives in /opt/stack. Go to the swift directory in the shell screen and edit your middleware module. Change to the directory where Object Storage is installed: $ cd /opt/stack/swift Create the ip_whitelist.py Python source code file: $ vim swift/common/middleware/ip_whitelist.py Copy the code in into ip_whitelist.py. The following code is a middleware example that restricts access to a container based on IP address as explained at the beginning of the section. Middleware passes the request on to another application. This example uses the swift "swob" library to wrap Web Server Gateway Interface (WSGI) requests and responses into objects for swift to interact with. When you're done, save and close the file. # vim: tabstop=4 shiftwidth=4 softtabstop=4 # Copyright (c) 2014 OpenStack Foundation # All Rights Reserved. # # Licensed under the Apache License, Version 2.0 (the "License"); you may # not use this file except in compliance with the License. You may obtain # a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the # License for the specific language governing permissions and limitations # under the License. import socket from swift.common.utils import get_logger from swift.proxy.controllers.base import get_container_info from swift.common.swob import Request, Response class IPWhitelistMiddleware(object): """ IP Whitelist Middleware Middleware that allows access to a container from only a set of IP addresses as determined by the container's metadata items that start with the prefix 'allow'. E.G. allow-dev=192.168.0.20 """ def __init__(self, app, conf, logger=None): self.app = app if logger: self.logger = logger else: self.logger = get_logger(conf, log_route='ip_whitelist') self.deny_message = conf.get('deny_message', "IP Denied") self.local_ip = socket.gethostbyname(socket.gethostname()) def __call__(self, env, start_response): """ WSGI entry point. Wraps env in swob.Request object and passes it down. :param env: WSGI environment dictionary :param start_response: WSGI callable """ req = Request(env) try: version, account, container, obj = req.split_path(1, 4, True) except ValueError: return self.app(env, start_response) container_info = get_container_info( req.environ, self.app, swift_source='IPWhitelistMiddleware') remote_ip = env['REMOTE_ADDR'] self.logger.debug("Remote IP: %(remote_ip)s", {'remote_ip': remote_ip}) meta = container_info['meta'] allow = {k:v for k,v in meta.iteritems() if k.startswith('allow')} allow_ips = set(allow.values()) allow_ips.add(self.local_ip) self.logger.debug("Allow IPs: %(allow_ips)s", {'allow_ips': allow_ips}) if remote_ip in allow_ips: return self.app(env, start_response) else: self.logger.debug( "IP %(remote_ip)s denied access to Account=%(account)s " "Container=%(container)s. Not in %(allow_ips)s", locals()) return Response( status=403, body=self.deny_message, request=req)(env, start_response) def filter_factory(global_conf, **local_conf): """ paste.deploy app factory for creating WSGI proxy apps. """ conf = global_conf.copy() conf.update(local_conf) def ip_whitelist(app): return IPWhitelistMiddleware(app, conf) return ip_whitelist There is a lot of useful information in env and conf that you can use to decide what to do with the request. To find out more about what properties are available, you can insert the following log statement into the __init__ method: self.logger.debug("conf = %(conf)s", locals()) and the following log statement into the __call__ method: self.logger.debug("env = %(env)s", locals()) To plug this middleware into the swift Paste pipeline, you edit one configuration file, /etc/swift/proxy-server.conf: $ vim /etc/swift/proxy-server.conf Find the [filter:ratelimit] section in /etc/swift/proxy-server.conf, and copy in the following configuration section after it: [filter:ip_whitelist] paste.filter_factory = swift.common.middleware.ip_whitelist:filter_factory # You can override the default log routing for this filter here: # set log_name = ratelimit # set log_facility = LOG_LOCAL0 # set log_level = INFO # set log_headers = False # set log_address = /dev/log deny_message = You shall not pass! Find the [pipeline:main] section in /etc/swift/proxy-server.conf, and add ip_whitelist after ratelimit to the list like so. When you're done, save and close the file: [pipeline:main] pipeline = catch_errors gatekeeper healthcheck proxy-logging cache bulk tempurl ratelimit ip_whitelist ... Restart the swift proxy service to make swift use your middleware. Start by switching to the swift-proxy screen: Press Ctrl A followed by 3. Press Ctrl C to kill the service. Press Up Arrow to bring up the last command. Press Enter to run it. Test your middleware with the swift CLI. Start by switching to the shell screen and finish by switching back to the swift-proxy screen to check the log output: Press  Ctrl A followed by 0. Make sure you're in the devstack directory: $ cd /root/devstack Source openrc to set up your environment variables for the CLI: $ source openrc Create a container called middleware-test: $ swift post middleware-test Press Ctrl A followed by 3 to check the log output. Among the log statements you'll see the lines: proxy-server Remote IP: my.instance.ip.address (txn: ...) proxy-server Allow IPs: set(['my.instance.ip.address']) (txn: ...) These two statements are produced by our middleware and show that the request was sent from our DevStack instance and was allowed. Test the middleware from outside DevStack on a remote machine that has access to your DevStack instance: Install the keystone and swift clients on your local machine: # pip install python-keystoneclient python-swiftclient Attempt to list the objects in the middleware-test container: $ swift --os-auth-url=http://my.instance.ip.address:5000/v2.0/ \ --os-region-name=RegionOne --os-username=demo:demo \ --os-password=devstack list middleware-test Container GET failed: http://my.instance.ip.address:8080/v1/AUTH_.../ middleware-test?format=json 403 Forbidden   You shall not pass! Press Ctrl A followed by 3 to check the log output. Look at the swift log statements again, and among the log statements, you'll see the lines: proxy-server Authorizing from an overriding middleware (i.e: tempurl) (txn: ...) proxy-server ... IPWhitelistMiddleware proxy-server Remote IP: my.local.ip.address (txn: ...) proxy-server Allow IPs: set(['my.instance.ip.address']) (txn: ...) proxy-server IP my.local.ip.address denied access to Account=AUTH_... \ Container=None. Not in set(['my.instance.ip.address']) (txn: ...) Here we can see that the request was denied because the remote IP address wasn't in the set of allowed IPs. Back in your DevStack instance on the shell screen, add some metadata to your container to allow the request from the remote machine: Press Ctrl A followed by 0. Add metadata to the container to allow the IP: $ swift post --meta allow-dev:my.local.ip.address middleware-test Now try the command from Step 10 again and it succeeds. There are no objects in the container, so there is nothing to list; however, there is also no error to report. Functional testing like this is not a replacement for proper unit and integration testing, but it serves to get you started. testing functional testing functional testing You can follow a similar pattern in other projects that use the Python Paste framework. Simply create a middleware module and plug it in through configuration. The middleware runs in sequence as part of that project's pipeline and can call out to other services as necessary. No project core code is touched. Look for a pipeline value in the project's conf or ini configuration files in /etc/<project> to identify projects that use Paste. When your middleware is done, we encourage you to open source it and let the community know on the OpenStack mailing list. Perhaps others need the same functionality. They can use your code, provide feedback, and possibly contribute. If enough support exists for it, perhaps you can propose that it be added to the official swift middleware.

Many OpenStack projects allow for customization of specific features using a driver architecture. You can write a driver that conforms to a particular interface and plug it in through configuration. For example, you can easily plug in a new scheduler for Compute. The existing schedulers for Compute are feature full and well documented at Scheduling. However, depending on your user's use cases, the existing schedulers might not meet your requirements. You might need to create a new scheduler. customization OpenStack Compute (nova) Scheduler schedulers customization of DevStack customizing OpenStack Compute (nova) scheduler To create a scheduler, you must inherit from the class nova.scheduler.driver.Scheduler. Of the five methods that you can override, you must override the two methods marked with an asterisk (*) below: update_service_capabilities hosts_up group_hosts * schedule_run_instance * select_destinations To demonstrate customizing OpenStack, we'll create an example of a Compute scheduler that randomly places an instance on a subset of hosts, depending on the originating IP address of the request and the prefix of the hostname. Such an example could be useful when you have a group of users on a subnet and you want all of their instances to start within some subset of your hosts. This example is for illustrative purposes only. It should not be used as a scheduler for Compute without further development and testing. security issues scheduler example When you join the screen session that stack.sh starts with screen -r stack, you are greeted with many screen windows: 0$ shell*  1$ key  2$ horizon  ...  9$ n-api  ...  14$ n-sch ... shell A shell where you can get some work done key The keystone service horizon The horizon dashboard web application n-{name} The nova services n-sch The nova scheduler service The code for OpenStack lives in /opt/stack, so go to the nova directory and edit your scheduler module. Change to the directory where nova is installed: $ cd /opt/stack/nova Create the ip_scheduler.py Python source code file: $ vim nova/scheduler/ip_scheduler.py The code in is a driver that will schedule servers to hosts based on IP address as explained at the beginning of the section. Copy the code into ip_scheduler.py. When you're done, save and close the file. # vim: tabstop=4 shiftwidth=4 softtabstop=4 # Copyright (c) 2014 OpenStack Foundation # All Rights Reserved. # # Licensed under the Apache License, Version 2.0 (the "License"); you may # not use this file except in compliance with the License. You may obtain # a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the # License for the specific language governing permissions and limitations # under the License. """ IP Scheduler implementation """ import random from oslo.config import cfg from nova.compute import rpcapi as compute_rpcapi from nova import exception from nova.openstack.common import log as logging from nova.openstack.common.gettextutils import _ from nova.scheduler import driver CONF = cfg.CONF CONF.import_opt('compute_topic', 'nova.compute.rpcapi') LOG = logging.getLogger(__name__) class IPScheduler(driver.Scheduler): """ Implements Scheduler as a random node selector based on IP address and hostname prefix. """ def __init__(self, *args, **kwargs): super(IPScheduler, self).__init__(*args, **kwargs) self.compute_rpcapi = compute_rpcapi.ComputeAPI() def _filter_hosts(self, request_spec, hosts, filter_properties, hostname_prefix): """Filter a list of hosts based on hostname prefix.""" hosts = [host for host in hosts if host.startswith(hostname_prefix)] return hosts def _schedule(self, context, topic, request_spec, filter_properties): """Picks a host that is up at random.""" elevated = context.elevated() hosts = self.hosts_up(elevated, topic) if not hosts: msg = _("Is the appropriate service running?") raise exception.NoValidHost(reason=msg) remote_ip = context.remote_address if remote_ip.startswith('10.1'): hostname_prefix = 'doc' elif remote_ip.startswith('10.2'): hostname_prefix = 'ops' else: hostname_prefix = 'dev' hosts = self._filter_hosts(request_spec, hosts, filter_properties, hostname_prefix) if not hosts: msg = _("Could not find another compute") raise exception.NoValidHost(reason=msg) host = random.choice(hosts) LOG.debug("Request from %(remote_ip)s scheduled to %(host)s" % locals()) return host def select_destinations(self, context, request_spec, filter_properties): """Selects random destinations.""" num_instances = request_spec['num_instances'] # NOTE(timello): Returns a list of dicts with 'host', 'nodename' and # 'limits' as keys for compatibility with filter_scheduler. dests = [] for i in range(num_instances): host = self._schedule(context, CONF.compute_topic, request_spec, filter_properties) host_state = dict(host=host, nodename=None, limits=None) dests.append(host_state) if len(dests) < num_instances: raise exception.NoValidHost(reason='') return dests def schedule_run_instance(self, context, request_spec, admin_password, injected_files, requested_networks, is_first_time, filter_properties, legacy_bdm_in_spec): """Create and run an instance or instances.""" instance_uuids = request_spec.get('instance_uuids') for num, instance_uuid in enumerate(instance_uuids): request_spec['instance_properties']['launch_index'] = num try: host = self._schedule(context, CONF.compute_topic, request_spec, filter_properties) updated_instance = driver.instance_update_db(context, instance_uuid) self.compute_rpcapi.run_instance(context, instance=updated_instance, host=host, requested_networks=requested_networks, injected_files=injected_files, admin_password=admin_password, is_first_time=is_first_time, request_spec=request_spec, filter_properties=filter_properties, legacy_bdm_in_spec=legacy_bdm_in_spec) except Exception as ex: # NOTE(vish): we don't reraise the exception here to make sure # that all instances in the request get set to # error properly driver.handle_schedule_error(context, ex, instance_uuid, request_spec) There is a lot of useful information in context, request_spec, and filter_properties that you can use to decide where to schedule the instance. To find out more about what properties are available, you can insert the following log statements into the schedule_run_instance method of the scheduler above: LOG.debug("context = %(context)s" % {'context': context.__dict__}) LOG.debug("request_spec = %(request_spec)s" % locals()) LOG.debug("filter_properties = %(filter_properties)s" % locals()) To plug this scheduler into nova, edit one configuration file, /etc/nova/nova.conf: $ vim /etc/nova/nova.conf Find the scheduler_driver config and change it like so: scheduler_driver=nova.scheduler.ip_scheduler.IPScheduler Restart the nova scheduler service to make nova use your scheduler. Start by switching to the n-sch screen: Press Ctrl A followed by 9. Press Ctrl A followed by N until you reach the n-sch screen. Press Ctrl C to kill the service. Press Up Arrow to bring up the last command. Press Enter to run it. Test your scheduler with the nova CLI. Start by switching to the shell screen and finish by switching back to the n-sch screen to check the log output: Press  Ctrl A followed by 0. Make sure you're in the devstack directory: $ cd /root/devstack Source openrc to set up your environment variables for the CLI: $ source openrc Put the image ID for the only installed image into an environment variable: $ IMAGE_ID=`nova image-list | egrep cirros | egrep -v "kernel|ramdisk" | awk '{print $2}'` Boot a test server: $ nova boot --flavor 1 --image $IMAGE_ID scheduler-test Switch back to the n-sch screen. Among the log statements, you'll see the line: 2014-01-23 19:57:47.262 DEBUG nova.scheduler.ip_scheduler \ [req-... demo demo] Request from 162.242.221.84 \ scheduled to devstack-havana \ _schedule /opt/stack/nova/nova/scheduler/ip_scheduler.py:76 Functional testing like this is not a replacement for proper unit and integration testing, but it serves to get you started. A similar pattern can be followed in other projects that use the driver architecture. Simply create a module and class that conform to the driver interface and plug it in through configuration. Your code runs when that feature is used and can call out to other services as necessary. No project core code is touched. Look for a "driver" value in the project's .conf configuration files in /etc/<project> to identify projects that use a driver architecture. When your scheduler is done, we encourage you to open source it and let the community know on the OpenStack mailing list. Perhaps others need the same functionality. They can use your code, provide feedback, and possibly contribute. If enough support exists for it, perhaps you can propose that it be added to the official Compute schedulers.

The dashboard is based on the Python Django web application framework. The best guide to customizing it has already been written and can be found at Building on Horizon. Django Python dashboard DevStack customizing dashboard customization dashboard

When operating an OpenStack cloud, you may discover that your users can be quite demanding. If OpenStack doesn't do what your users need, it may be up to you to fulfill those requirements. This chapter provided you with some options for customization and gave you the tools you need to get started.