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Customizing Object Storage (Swift) Middleware

OpenStack Object Storage, known as swift when reading the code, is based on the Python Paste framework. The best introduction to its architecture is on Read The Docs. 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.

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.

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:


A shell where you can get some work done


The keystone service


The horizon dashboard web application


The swift services

To create the middleware and plug it in through Paste configuration:

All of the code for OpenStack lives in /opt/stack. Go to the swift directory in the shell screen and edit your middleware module.

  1. Change to the directory where Object Storage is installed:

    $ cd /opt/stack/swift
  2. Create the ip_whitelist.py Python source code file:

    $ vim swift/common/middleware/ip_whitelist.py
  3. Copy the code as shown below 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=
        def __init__(self, app, conf, logger=None):
            self.app = app
            if logger:
                self.logger = logger
                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)
                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())
            self.logger.debug("Allow IPs: %(allow_ips)s",
                              {'allow_ips': allow_ips})
            if remote_ip in allow_ips:
                return self.app(env, start_response)
                    "IP %(remote_ip)s denied access to Account=%(account)s "
                    "Container=%(container)s. Not in %(allow_ips)s", locals())
                return Response(
                    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()
        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())
  4. 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
  5. Find the [filter:ratelimit] section in /etc/swift/proxy-server.conf, and copy in the following configuration section after it:

    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!
  6. 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 = catch_errors gatekeeper healthcheck proxy-logging cache bulk tempurl ratelimit ip_whitelist ...
  7. Restart the swift proxy service to make swift use your middleware. Start by switching to the swift-proxy screen:

    1. Press Ctrl+A followed by 3.

    2. Press Ctrl+C to kill the service.

    3. Press Up Arrow to bring up the last command.

    4. Press Enter to run it.

  8. 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:

    1. Press  Ctrl+A followed by 0.

    2. Make sure you’re in the devstack directory:

      $ cd /root/devstack
    3. Source openrc to set up your environment variables for the CLI:

      $ . openrc
    4. Create a container called middleware-test:

      $ swift post middleware-test
    5. Press Ctrl+A followed by 3 to check the log output.

  9. 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.

  10. Test the middleware from outside DevStack on a remote machine that has access to your DevStack instance:

    1. Install the keystone and swift clients on your local machine:

      # pip install python-keystoneclient python-swiftclient
    2. 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!
  11. 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.

  12. Back in your DevStack instance on the shell screen, add some metadata to your container to allow the request from the remote machine:

    1. Press Ctrl+A followed by 0.

    2. Add metadata to the container to allow the IP:

      $ swift post --meta allow-dev:my.local.ip.address middleware-test
    3. 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.

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.