The DETER ASPI is really an interface with two sides, an outward facing side (the testbed SPI) that allows people to manage resources on the testbed and an inward facing side (the containers SPI) that coordinates the containers that make up an experiment environment. This document defines these interfaces and documents how to use them. It is a living document that will gain detail as the specification grows and implementations are put into service.
The testbed API is responsible for managing the following things:
The testbed SPI enables users to ask a DETER testbed to do things for them. It will generally be called from a more user-friendly front end, tuned to the user's experience and goals, such as the evoloving DETER Beginners Interface.
The containers API is used by the DETER control system to manage the resources that make up an experimental topology in progress. The goal of this API is to take raw resources inside the testbed that have been allocated using the testbed API, and configure them into a usable environment. Each logical element of an experiment (a computer, a router, etc.) is represented by a container which must be managed by DETER.
Managing a container consists of:
We discuss the testbed SPI and then the containers SPI. Then we discuss some initial implementation details and present a roadmap for development.
The testbed SPI manipulates a few entities to provide the experimentation environment. This section discusses the key abstractions of the testbed SPI and how they work together to create an experimental environment.
A user is a researcher who uses the DETER testbed. They request testbed services and allocate testbed resources. Users are the actors that make things happen through test testbed SPI.
Each user is identified by a unique string, their userid. Userids are assigned when the user is created on the testbed and guaranteed to be unique.
In addition to the user identifier DETER keeps meta-data about users. Currently that meta-data consists of:
A user identifies themselves to the testbed SPI by proving that they hold a specific public/private keypair. An initial such keypair is issued when the user is created, and a user can acquire another valid pair at any time by proving they know their password. Generally those pairs are short-lived to guard against loss or theft, but the password is administered using local testbed policies.
DETER groups users for two main reasons: to distribute the time costs of administration and to facilitate collaborative use of DETER's resources. The first is accomplished through the Project abstraction and the second through the Circle abstraction.
Projects are groups of users who can access testbed resources. They correspond to such real-world groups as classes or research projects. Each project has an owner, vetted by DETER staff, who can then add users to the project at their discretion. Such users have access to the DETER testbed. This is close in spirit to an Emulab project, but shorn of its access control implications.
A project always has an owner, the user vetted by DETER staff. Ownership can be changed, but only by the owner.
When a user is added to a project, their rights are also defined within that project. The rights are:
Each project has a profile attached to it, as a user does, and that profile can be expanded to include other attributes.
When a researcher wants to start a project on DETERlab, the researcher creates a user and requests a project. Though the testbed API sees this as two steps, the user interface presented by a web page would roll these two steps together. A user sees it as a single application page.
The project is created but unapproved and cannot do anything. When the group responsible for vetting projects approves the project, its state is changed (to approved) and the owner can now add other users and use testbed resources. (Each project has a circle linked to it that controls project members access to testbed resources.)
When a new user applies to join the testbed, a user is created that can only set its password or apply to create or join a project. When a user applies to join a project, all project members who can add that user are notified. Any one of them can accept the user and set their permissions. By accepting that user the project takes some responsibility for them. If that user misbehaves, the project owner will be contacted as well as the user.
If a user is removed from all projects, they return to a powerless state.
Circles are groups of users. They are used to confer rights to groups of users, identify groups of users, and influence how resources are configured when experiments are realized on the testbed. Circles are intended to be lightweight and encourage collaboration inside a project or across projects. This is a more general use of grouping than an Emulab testbed.
A circle always has an owner, the user responsible for its creation. Ownership can be changed, but only by the owner.
Circle names are scoped one of two ways, by prefixing them with either the uid of the user that created it, or a project that the creating user is a member of. The right to create circles with the project's prefix is controlled by a user's permissions in the project. Because uids and project names are unique across the testbed, circle names are unique when prefixed. The names written as prefix:circle.
When a user is added to a circle, their rights are also defined within that circle. The rights are:
Each circle has a profile attached to it, as a user does, and that circle can be expanded to include other attributes.
Each user in an approved project is a member of at least two circles: a circle attached to the project (created and owned by the owner of the project in the project's name space) and a single-user circle owned (and created by) the uid. A user bob in project newclass will be a member of the circle bob:bob and newclass:newclass.
Bob will have the right to realize experiments in the bob:bob circle - that is bob can create experiments that only bob can access. Bob will also have whatever rights the owner of the newclass project gave bob when he joined. If bob created the newstuff project, bob will have all rights in the newstuff:newstuff project. No user has the right to add or remove users from their single-user circle.
Circles are used to control sharing as well. If bob and alice are made a team in newclass, the owner of that project, e.g., their instructor or teaching assistant, can make them a circle under the project's namespace. bob and alice may be made members of newclass:team1. Now experiments realized in that circle will be accessible to bob and alice.
A user can create circles at will, but can only add users to a circle with their consent. Because circles enable users to share resources (e.g., local files) the desire to share must be mutual.
The circle linked to a project is manipulated through the project, not as a circle. Users added or removed to a project are added to or removed from its linked circle. Permissions are also manipulated through the project interface. A simple project may never need to create additional circles.
All of the testbed API is ultimately geared toward the creation of experiments. An experiment contains many aspects that define its environment and operation. An aspect is a user-defined piece of data that is used to influence the testbed's operation. Some aspects are understood by the base testbed, and some must be interpreted by code supplied by the user. Initially the prototype understands only a few aspects. These include:
Not all experiments in the sense of the API data structure will have all these elements. Testbeds are often used to create an environment in which to try ideas out and explore ideas without intending to reproduce the experience. The other end of the spectrum is rigorous, repeatable hypothesis testing. The API supports both by allowing some of these aspects to be omitted for some experiments (in the API sense).
This API is primarily concerned with:
We call the process of constructing the experiment's environment realizing the experiment.
In order to support experiments that are making minimal use of experiment control systems, the API allows a user to manipulate a realized experiment, including
These interfaces use filtering and graph analysis to present useful views of large experiments.
When realizing the experiment, the testbed uses the containers API to configure and control the hardware and software that create the environment.
The containers API is responsible for allocating resources to an experiment and configuring that hardware in ways appropriate for the user's goals - realizing it.
The key abstraction for realizing an experiment is the container. A container holds some of a physical resource's computational and networking power and uses it to create part of the experiment at a level of realism appropriate to the researcher's goals. A researcher who is interested in end-system behavior will not put very much computational power into realizing the routers that forward packets, but a lot into realizing end systems.
The containers API coordinates:
This API supports communication between the testbed control system and the containers that make up an experiment being realized (and after it is realized).
A clear kind of container is a computer running a virtual machine monitor that partitions its CPU resources between virtual machines. This is a very useful kind of container, but not the only one. The containers interface is intended to support new forms of computer virtualization, efficient network simulation, or new kinds of physical hardware that can be part of testbeds.
To support these goals operations that the testbed can perform on a container are simple and can be specialized. In particular, the operations guaranteed to work on any container are:
A container can be in the following states:
Containers report state in response to a describe operation and can also spontaneously report changes in state to the testbed.
Generally a container's life cycle looks like:
From that point the testbed can issue Clean, Configure, and Start commands to adjust the container state and operation.
Resources are the physical and conceptual objects managed by the testbed that are used to build experimental environments. They are the computers, network ports, externally routable addresses, virtual machine images, et al. from which experiments are constructed.
Resources are a class of objects that are user to build experiments. Now there are are a few well known resources that are visible to the SPI, but generic resource objects are also supported by the SPI and provide a way to integrate new building blocks. Some of the specialized resources are:
Access to and configuration of resources is affected by the project(s) a user is acting as a member of. When a user requests resources, thay specify the projects under which they are requesting them. A user requesting resources as a member of a project representing a university class may have access to different resources than one acting as a member of the testbed administration. How membership affects the resources a group can claim is set by testbed policy?.
In addition, the membership in projects controls how resources will be configured. A resource in use by a particular project will generally be configured to be accessible to all members of that project. A student who allocates resources as a member of a small design group while implementing a class project may later allocate resources as a member of the whole class when presenting the work to the class's TA and professor.
The most common form of container specialization is the configuration format that the container expects. We have defined formats for containers that look like computers that define accounts, filesystems, software installations, etc. Other configuration formats will evolve and move into the mainstream.
In addition we define low-level commands in an experiment description that bind a configuration message content to a node in an experiment. This allows new container configurations to be communicates even when the testbed does not understand them.
In addition to custom configuration systems, containers can export custom operations. For example, some virtual machines support snapshotting their state. That can be useful to experimenters. Again containers can advertise operations that the testbed is unaware of and the testbed API presents a way for users to pass a request through to a container directly.
To understand how the pieces above fit together, here is an example of a researcher using DETER.
A person has an idea for research they would like to to conduct on DETER. That researcher accesses a DETER user interface - for example the DETER web interface - and fills out a form that gathers information about them and their proposed research. The web interface translates this into a request to create a user and then to create a vetting project for that user. The information about the research is routed to the DETER administration.
After the DETER administration decides that the research is reasonable and meets their criteria, they authorize creation of the vetting project. The administration sends the user e-mail telling them they can use DETER. Additionally the testbed may add the new user to a project for new users or other projects for researchers in similar fields.
When the user visits the DETER web interface, it notices that the user is a member of the new users project and presents an opportunity to take a tutorial. In addition, the user has access to sample experiments accessible to users in the new users project. Working from the tutorial and documentation and starting from a sample experiment, the user may create a new experiment with an environment, constraints, procedure and data collection specced out.
The web interface uses the testbed API to review an experiment in the new users project, copy it to the user's vetting project and edit the new experiment to meet the user's goals.
The user then realizes the experiment using the testbed API, uses the experiment control API - usually MAGI - to carry out the experiment and collect the data. When the experiment is complete, the testbed API is used to release resources.
Now the user assesses the data, and may go off to publish results or create a new experiment from this one that tests a different hypothesis or something else.
From here, readers may be interested in the