BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:Composition and Inheritance in Declarative Configuration Languages - Paul Anderson\, University of Edinburgh DTSTART:20170518T090000Z DTEND:20170518T100000Z UID:TALK72543@talks.cam.ac.uk CONTACT:Microsoft Research Cambridge Talks Admins DESCRIPTION:Configuring large computing installations is a difficult probl em -- there are many different subsystems involved\, all with their own la nguage\, and many different people with an interest in overlapping aspects of the overall configuration. Deploying and maintaining a configuration w hich reliably meets everyone's "higher-level" requirements is hard\, and configuration errors are responsible for a significant proportion of syste m failures.\n\nAlmost all large installations use some type of "configurat ion tool" in an attempt to automate and unify the process. These often inv olve some kind of custom specification language\, which is often claimed t o be "declarative". But all practical configuration languages have develop ed in very informal ways\, with a complex semantics which are error-prone and difficult to use. Declarative configuration languages in particular\, are quite different from programming languages\, and have not been widely studied in any formal way\, despite their critical role in most large infr astructures.\n\nFor a long time\, I have been interested in understanding the overall configuration process\, and particularly in designing more usa ble languages\, which provide specific features to support this in a clear in and correct way. Although there is little directly related work\, thi s has led to interesting connections with a number of other areas\, two of which have been the subject of previous Microsoft Research Phd Scholarshi ps:\n\n- The use of constraint-based specifications[1] (with Andy Gordon) particularly the novel use of these of these to support conflict-free comp osition of partial specifications from different stake-holders\n\n- The us e of provenance techniques (from the database field) to track the dependen cies between final configuration parameters and the source specifications which affect them[2] (with Dimitrios Vytiniotis). This has implications fo r fault diagnosis\, and security (which is not addressed well\, if at all\ , in current languages)\, and it suggests new ways of resolving potential conflicts.\n\nI have also been involved in the deployment of the resulting configurations\, particularly distributed agent-based approaches using au tomated planning.\n\nRecently\, we have been trying to formalise the seman tics of practical declarative configuration languages[3\,4] and the diffic ulty of this has highlighted some of the reasons why this type of language has acquired an (unnecessary) reputation for complexity. This has led to an interest in human-factors work on the usability of configuration langua ges[5]\, and it seems that these considerations should be a fundamental pa rt of the design process for any new language - I have a (currently unfund ed) proposal for a Phd in this area[6].\n\nI plan to use some recent work on composition of configurations as the focus for a talk which will draw o n various aspects of this previous work. The short note [7] is an accessi ble description of this for a non-specialist audience. However\, I would l ike to share my experiences with the configuration problem in general to s ee if there was any further possible synergy\, and I would be happy to foc us more on any aspects which may be of interest\, and to discuss anything else which may potentially be of common interest.\n\nPaul Anderson \nhttp://homepages.inf.ed.ac.uk/dcspaul\n\n(*) SOME CONFIGURAT ION TOOLS\n\n- "Puppet" (https://puppetlabs.com/) is probably the most com mon "declarative" tool.\n\n- "Cfengine" (http://cfengine.com/) was one of the first-generation tools which claimed to be "declarative".\n\n- "SmartF rog" (http://www.smartfrog.org/) probably has the cleanest semantics\, but has never been widely used outside of HP.\n\n- "LCFG" (http://www.lcfg.or g/) was developed here in Informatics\, and is probably the oldest "declar ative" tool. But the "language" is very primitive\, and the tool is not wi dely used outside of the University.\n\n- Chef (https://www.chef.io/) is d erived from Puppet\, but takes a more imperative approach\, probably due t o the apparent difficulty of using the Puppet language.\n\n- "Ansible" (ht tps://www.ansible.com/) is a more imperative approach focussing on "tasks" which are executed in order" - this is claimed to be more simple than a d eclarative approach.\n\n- Microsoft Powershell (https://msdn.microsoft.com /en-us/powershell/mt173057.aspx) is an an imperative language and framewor k for scripting configuration changes\, however DSC ("desired state config uration") introduces some declarative features.\n\nREFERENCES\n\nSummary: The short note [7] is an informal introduction to the composition problem which avoids the distracting details of ``real'' configurations\, and the technicalities of ``real'' configuration languages. [4] is a good introduc tion to the difficulties and complexities of ``real'' languages\, and the more formal work on the semantics. [2] is a short position paper which ill ustrates some usability problems and motivates the current work provenance work.\n\n[1] Constraint-based autonomic configuration\n2013 Self-adaptive and self-organizing systems conference (SASO)\, September 2013\nJohn A He wson & Paul Anderson & Andrew D Gordon\nhttp://homepages.inf.ed.ac.uk/dcsp aul/homepage/live/pdf/saso-2013.pdf\n\n[2] Toward provenance-based securit y for configuration languages\nThe 4th Usenix workshop on the theory and p ractice of provenance\, June 2012\nPaul Anderson & James Cheney\nhttp://ho mepages.inf.ed.ac.uk/dcspaul/homepage/live/pdf/tapp12-final15.pdf\n\n[3] A formal semantics for the SmartFrog configuration language\nJournal of Net work and Systems Management\nPaul Anderson & Herry Herry\nhttp://homepages .inf.ed.ac.uk/dcspaul/homepage/live/pdf/sfsemantics.pdf\n\n[4] μPuppet: A Declarative Subset of the Puppet Configuration Language\nTechnical report \, December 2016\nPaul Anderson\, James Cheney\, Weili Fu & Roly Perera\nh ttp://homepages.inf.ed.ac.uk/dcspaul/homepage/live/pdf/arxiv-puppet.pdf\n\ n[5] Usability of System Configuration Languages: Confusion caused by Orde ring\nAdele Mikoliunaite\nhttp://homepages.inf.ed.ac.uk/dcspaul/homepage/l ive/pdf/msc_20162088.pdf\n\n[6] Usability of System Configuration Language s - IGS Studentship Proposal\nhttp://homepages.inf.ed.ac.uk/dcspaul/homepa ge/live/pdf/usability-phd.pdf\n\n[7] Composition in the L3 Configuration L anguage\nhttp://homepages.inf.ed.ac.uk/dcspaul/homepage/live/pdf/l3composi tion.pdf\n\n LOCATION:Small Lecture Room \, Microsoft Research Ltd\, 21 Station Road\, Cambridge\, CB1 2FB END:VEVENT END:VCALENDAR