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Emulab Source Tree Map

Emulab Source Tree Map

This file documents roughly the contents of our source tree as of April, 2003. Some of the entries in here are per-script, others are for a group of scripts, in which case the documentation inside the individual scripts should be sufficient explanation. The end of the file also has some overview-ish stuff about abstractions and things like that.

[This file maintained by]

For big picture and some details, read the OSDI'02 paper, in doc/papers/netbed-osdi02* and on the Web.


Account Management

  • unix accounts
    • unix group management (per-proj and per-group)
  • ssh key distribution
  • sfs key distribution
  • account permissions (web only, ron/wa, root/non-root, etc.)
  • emulab permissions
    • control of hardware/hw config.
    • administrative control
  • hierarchical organization
    • delegation at all levels
    • trust models and their security impact


Assign (resource allocation algorithms)

  • the Testbed Mapping Problem: read draft of our upcoming CCR paper in doc/papers
    • NP Hard
    • in some ways, constraint satisfaction problem
      • but more, because not all satisfactory solutions are equal
    • time constraints: we're an interactive system, and need to perform on interactive timescales - a few seconds max to get a good answer
    • variation in wide area
      • soft matching
      • complicated more by fact that we can combine the unknown (wide-area link) with something we control (traffic shaping)
  • Emulab solution
    • many "valid" solutions, but difference between near-optimal and random valid soln. is huge and important
    • sim. annealing core
    • highly optimized
      • clever domain specific tricks
      • main purpose is to conserve scarce resources (nodes, interswitch bandwidth, soon special hw like GigE)
    • lots of parameters, not always clear how to tune them
  • Netbed solution
    • typically no exact match, just some that may be closer than others - very fuzzy matching
    • genetic algo. core
    • not as highly developed yet, but meets our needs
    • main purpose is to find a real-world overlay that matches the supplied topology as closely as possible


Apache web server configuration


Capture/console (node consoles - "'zero-penalty' remote research")

  • serial line consoles to nodes replace kbd/vga
  • fine-grained access control
    • changes quickly when node changes "ownership"
  • simple, secure remote access
    • ACLs, authenticated ssl tunnel program + standard telnet client


CD-ROM (remote node mgmt/robustness, adding nodes to the system)

  • simple to add a node
  • fallback boot method (CD-ROM) when disk is hozed
  • path for self-update and disk reimaging
  • goal is to reduce need for human intervention whenever possible


Collaboration Tools

  • Allows users to more easily coordinate experimentation
  • Adapted different services for Emulab.
  • Jabber
  • Trac
  • Mailman
  • CVS


Database (centralized store for persistent shared system state)

  • lots o' stuff here
  • most stuff falls into one of several categories
    • semi-permanant hw setup info (wires, ifaces, nodes, outlets)
    • current hardware configs (reservations, ifaces, vlans, etc)
    • semi-permanant sw setup info (disk images, OS's, etc.)
    • current sw setup (traffic shaping, trafgen, routing, etc.)
    • virtualized expt info (topology, config, etc)
    • administrative info (users, groups, projects, etc.)
    • misc. config bits and logging
  • sw engineering issues
    • db schema must match sw build


Delay Nodes

  • Used to shape/delay traffic to emulate different kinds of links


DHCP Daemon Configuration


Event system (distributed event coordination/communication)

  • "Elvin" publish/subscribe system underneath (imported from elsewhere)
  • used in several directions
    • emulab to nodes/programs
    • nodes to emulab
    • programs on emulab server to each other
    • can be nodes to nodes too
  • delay agent
    • coordinated control of traffic shaping
    • changes can initiate anywhere
      • automatic timed changes from emulab
      • manual changes from emulab server or a node
    • allows for reactive traffic shaping, trace playback, etc.
  • nsetrafgen
    • control of NSE simulators and their traffic generation
  • program agent
    • start/stop arbitrary program
    • timed or manual, and allows reactivity
  • event scheduler
    • controls timed events
    • may be submitted apriori or during a run
  • stated uses it heavily, but is described elsewhere
  • tevc/tevd
    • simple command line client for use on any server or node
  • trafgen
    • traffic generation via TG toolkit
    • patched to allow control via events


Stated ("state-dee") - node state management daemon

  • listens for node state events
    • performs triggered actions
    • watches for problems/timeouts
      • sends notifications at times
    • updates the database with current state
  • watches how nodes reboot, reload, etc
  • several "state machines" (operational modes) define what is correct
    • each node is somewhere in some state machine always
  • reports successful boots, reloads, etc.


Firewall Configuration

  • Protects
    • nodes from the world
    • world from the nodes
    • servers from the nodes


Emulab Client for Flash Drives


Switch Configuration Files


Three-dimensional Visualization for Emulab Topologies


Testing framework for client images


Installation (emulab cluster site configuration tools)

  • for making more emulabs
  • mostly automated install process
    • FreeBSD "port"/"meta-port"-style install script
    • installs dependencies as needed
    • performs emulab-specific install tasks
  • one for configuring a "boss" node (secure server)
  • one for configuring an "ops" node (public server)


ipod/apod (node control without power control hardware)

  • "ICMP Ping-Of-Death" and big brother, "Authenticated Ping-Of-Death"
  • reboot pingable but hung node without external intervention
  • adds robustness and greater control
  • especially important where only other alternative is a human


Libaries (Software engineering?)

  • shared constants
  • common interfaces
  • database routines and abstractions
  • important for robust, maintainable software


Memory-filesystem used during frisbee loading


Client software to run on motes


DNS configuration files


Scripts to track node usage over time


OS tools (disk images, etc)

  • management of disk contents
  • image creation
    • imagezip
      • lots of cool tricks here - read the frisbee paper
  • image distribution/installation
    • frisbee
      • lots to say here... read the paper in USENIX'03 and doc/papers
    • growdisk - partition management on heterogeneous nodes
  • deltas
    • deprecated - dump/restore
    • with our incredible disk image tools, it is way faster to just reload the disk instead of checking it first
  • tarfile installation
    • easy changes without forcing a customized disk image


Patches on software packages adapting them for Emulab use


Flexlab - Dynamic and static path emulation extensions


ProtoGENI - Our prototype which implements the GENI API for federation


PXE/DHCP - node boot process

  • automatic database-driven control of nodes
  • can't assume anything about the disk
  • node always boots off of PXE so we get control
  • talk to the database (via bootinfo)
    • may be told to boot a tftp kernel or a specific partition
    • tftp kernels (often with Memory file systems) used for:
      • disk image creation/installation
      • NetBoot
      • OSKit kernels
  • in emulab disk images, nodes self-configure using a pull model
    • see also TMCD
  • progress monitored by stated


Boot scripts


Mobile Wireless Testbed



  • always conscious of threat model
  • segregate public server (ops)
  • limited shells on secure server
    • secure server trusted by all nodes
      • emulab performs config tasks on behalf of user
  • plasticwrap/paperbag - transparently run commands on secure server
  • suexec during web execution adds extra layer of security and permission checks
  • lastlogs
    • track logins on servers and nodes, report into main db
  • giving away root on the nodes causes issues
  • passwords
    • we enforce good ones via checkpass/cracklib
    • have expirations



  • monitor nodes
  • healthd - temperature, etc
  • slothd - activity measurements
    • detect tty, network, cpu activity and report it
    • low overhead
    • agile
      • extremely low latency in detecting new activity in an idle node
      • higher latency okay for detecting beginning of inactivity
        • when its active, stay out of the way...


Certificate Creation Scripts


Emulab Administration Tools



  • core of testbed software
  • primary focus: expt config tasks
    • and auxiliary functions necessary for expt config stuff
  • assign_wrapper
    • interface between db data representation and resource allocation algorithms. Call the solver and use the output to set up the database state that runs the rest of the process.
  • batch daemon
    • core of a pretty typical batch system
    • allows for more automation
      • submit expt even when no resources are avail., runs later
  • checkports - ?
  • console reset/setup
    • control console access (see also capture section)
  • db2ns - dump our db data rep back into an ns file
  • eventsys start/control
    • start up event schedulers for each expt - see event section
  • exports setup
    • control access to files via NFS on nodes
    • create an /etc/exports file based on current node "ownership" and group membership
    • controls access to all home dirs, proj dirs, and group dirs
  • frisbeelauncher
    • wrapper to set up a frisbee server when trying to load a disk
  • libaudit - track requests for certain control actions
  • libtbsetup - see libraries section
  • libtestbed - see libraries section
  • mkgroup/mkproj, rmgroup/rmproj, rmuser
    • manage users, groups, and projects (sync unix world to match db)
  • named_setup
    • set up dns subdomains for each expt
    • create aliases for each node that are consistent across swapins
  • node_control - change node sw setup params (boot params, startup)
  • node_reboot
    • reboot a node as gracefully as possible
    • try 'ssh reboot', IPOD, then power cycle, as needed.
  • node_update - push mounts/accounts changes to nodes
  • nscheck - syntax check an ns file for use in emulab
  • os_load - start a frisbee disk reload
  • os_select - configure node boot params
  • os_setup
    • major part of expt config
    • db says what nodes should be running, so make it happen
    • may load disks, then reboots nodes and waits for them to come up
  • portstats - diag. tool for switch port counters
  • power - power control program
  • ptopgen - generate description of currently available hw
  • reload_daemon
    • first-cut node manager
    • reload disks when nodes get freed
  • resetvlans - clear any vlans made up of a set of nodes
  • routecalc - generate shortest path routes for a topology
  • sched_reload - set up a disk reload for later
  • sched_reserve - set up a node to go to an expt when freed
  • setgroups - update unix groups file with current membership
  • sfskey update - sync live sfskey config with db config
  • snmpit - SNMP switch control
    • supports multiple switch types
    • configures VLANs into "links" and "LANs" in topologies
    • read other switch data (ie for portstats)
  • startexp/endexp - begin/end experiments
    • wrappers called from web
    • start takes a "new" expt and an ns file
      • prerun it and swap it in, and send mail, leaving "active" expt
    • end takes a expt that is "new", "swapped", "active", or "terminated"
      • swap out if needed, and tbend it, then clean up the last bits
  • staticroutes
    • take db topology info and pass it to routecalc to generate static shortest-path routes for the expt. Save result in db.
  • swapexp
    • called from web - swap in, out, or restart an expt.
    • performs some checks, some locking, and calls tbswap or tbrestart
  • tbprerun
    • parse an ns file into the database, fully preparing it for swapin
  • tbswap
    • swap an expt in or out
    • performs a long list of sw/hw setup tasks
  • tbend
    • end an expt that has been swapped out
    • clean out virtual state
  • tbreport
    • dump a report of the experiment's configuration (virt and phys)
  • tbresize
    • older interface for rudimentary expt editing
    • add nodes to an expt, either unconnected or in a LAN
  • tbrestart
    • restart an expt without completely swapping out and back in
    • restart event system, reset ready/startup/boot status, port cntrs
  • vnode_setup
    • called from os_setup
    • configures multiplexed virtual nodes
    • mechanism: ssh runs a script in on the disk
  • wanassign/wanlinksolve (see assign section)
  • wanlinkinfo - display info on wide-area nodes from db
  • checkpass - see security section
  • ns2ir
    • The Parser
    • similar to/based on ns parser
    • rewrote methods to put info into database
    • performs emulab-specific checks
    • we supply a library that they use to get access to emulab-specific commands


Testsuite (regression testing - software engineering?)

  • automated system runs lists of tests in different modes
    • modes are levels of reality
  • used for regression testing ("did we break something?")
    • and development ("does this new thing work?"
  • test mode (aka frontend mode):
    • all scripts run like normal, but whenever something would have touched hardware, assume it succeeded, and return
    • doesn't touch nodes/switches, etc, but does all the db changes
  • full mode:
    • reserve some nodes from the testbed
    • set up "redirect" for certain critical daemons
    • set up an alternate db, make our nodes the only free ones
    • run alternate daemons (or live daemons use alt. db for our nodes)
    • entire system runs like normal, but off of a separate installed set of scripts
  • very flexible
    • tests can modify db, run arbitrary scripts
    • simple to use in normal case
      • check that normal expt path runs w/o errors
  • work in progress:
    • use full mode to verify accuracy/precision of traffic shaping
    • some parts may evolve to a set of tests that we run quickly at after swapping in before turning it over to the user


Remote Serial Console Access


TMCD - Testbed Master Control Daemon

  • Server for node self-configuration
    • provides controlled access to the database
    • supports a pull model
    • recieves various reports/messages from nodes
  • TMCC - Testbed Master Control Client
    • currently supported on FreeBSD and Linux, and ported to OpenBSD
    • tool for nodes<->emulab communication
    • part of a set of node initialization scripts
  • Node self-configuration process
    • report "I'm alive"
    • update config scripts (currently via sup)
    • run the config, which sets up:
      • interfaces, accounts, mounts, agents, startup programs, testbed daemons, installs tarfiles/rpms/etc, starts ntp, traffic shaping, virtual nodes, routing (gated/ospf and static/manual routes), hostname, /etc/hosts, IPOD/APOD, sfs, etc.
    • used on local nodes and widearea nodes, as well as inside jails

tmcd/{freebsd/ixpboot/, linux/ixpboot/}

IXP (special hw resources) [not released due to Intel license restrictions]

  • use as testbed infrastructure
    • traffic shaping
  • use for experimentation
    • shared facil. gives more people access, increases usage
    • emulab is good environment w/many tools


Netbed Wide-area nodes

  • Most emulab abstractions have netbed wide-area counterpart
    • same methods/abstractions/tools used in LAN or WAN environment
    • easy to switch from a wide-area run to an emulated run (or simulated)
  • Boot process a little different
  • Many parallels to local area case
    • SFS instead of NFS for shared homedirs
    • Can set up links as tunnels with 192.168.* addresses
    • Accounts same (except for rootness)
    • Traffic generation


Tools (built for emulab, but useful outside of it too)

  • pcapper
    • traffic visualization tool
    • realtime tcl/tk graph of packets/throughput
    • categorized by traffic types


Utilities for Common Tasks



  • graphical view of topologies in the database


Wiki Management and Configuration

  • Documentation is handled through the wiki


Web Interface

  • Main configuration/administrative interface
  • Manage projects, groups, users
    • edit user info, ssh keys, sfs keys, etc.
    • push account updates to nodes
  • Control nodes/experiments
    • start/end/swap expts
    • control nodes, delays, etc.
    • NetBuild GUI for creating expts/nsfiles
    • node status/monitoring
  • Get info about Emulab/Netbed
    • even download a CD, and get a key to join Netbed
    • all the documentation
      • tutorials, FAQs, etc.
    • publications, photos, some of our users, etc.
  • manage project data
    • disk images, custom OS's, etc.
  • for admins etc, also provides web db access and cvs web access


XMLRPC - A programmatic interface to the Emulab API.

  • Experiment control
  • Alternative to Web Interface
  • Used as a backend for multiple graphical clients


Simulated Nodes

  • many nodes simulated inside NSE on a single phys. node
  • can interact with real network
  • traffic gen can happen inside
  • links, etc. all work like normal
  • Due to NS limitations/abstractions, lots of things in the real world don't have a parallel here

Multiplexed Nodes

  • many nodes run on one physical node, and appear as many individual nodes
  • Implemented with "jail" on FreeBSD, or "VServers" on Linux
  • Goal to be as close to normal physical nodes as possible
  • creates lots of issues with multiplexing of virtual links onto physical links
    • routing, demultiplexing, etc

Cross-cutting Abstractions

  • Four different environments
    • Emulab/emulation (dedicated phys.) nodes, wide-area nodes, simulated nodes, and multiplexed ("virtual") nodes
    • can mix and match in same expt
    • in many cases, same expt can run in any (or several) of the environments with few or no changes
  • Nodes
    • Emulated/emulab: dedicated physical nodes in a cluster
      • get root, can reboot, serial console, total control of node
        • including OS, disk imaging, etc.
    • Widearea: shared nodes, geographically distributed
      • get an account (non-root, typically)
      • sometimes get a jail / "virtual server"
      • less control (of OS, rebooting, etc.)
    • Simulated: nodes inside of an NS simulator
      • nodes are simulated, don't run an OS, etc.
      • functionality programmed via NS models
    • Multiplexed: jails / virtual servers on cluster nodes
      • Almost as real as emulation nodes
      • allows bigger scale, risks potential for side-effects
      • same level of control as emulation nodes
  • Links
    • Emulated/emulab:
      • completely controllable network characteristics
      • including LAN speeds or shaped links
      • isolated control network
      • very realistic, predictable, repeatable
    • Widearea:
      • network is the real/raw internet
      • tunnels are optionally configured
      • no separate control network
      • completely realistic, but unpredictable
    • Simulated:
      • links inside NSE (NS Emulator)
      • NSE does shaping
      • real and sim worlds can talk to each other
    • Multiplexed:
      • Same capabilities as normal emulated/emulab links
      • some tricks involved to get everything to work right