HOLACONF - Cloud Forward 2015 Conference From Distributed to Complete Computing HAMZA. in collaboration SAHLI with

Transcription

1 HOLACONF - Cloud Forward Conference From Distributed to Complete Computing HAMZA in collaboration SAHLI with Pr. Faiza BELALA and Dr. Chafia BOUANAKA LIRE Laboratory, Constantine II University-Abdelhamid Mehri

2 1. Introduc+on 2. Bigraphical Reac+ve Systems (BRS) 3. Modelling Cloud Systems and Their Elas+c Behavior 4. Reachability Checking 5. Conclusion 2

3 3

4 What is Cloud Compu+ng? According to NIST (*) «Cloud compu*ng is a model for enabling ubiquitous, convenient, on- demand network access to a shared pool of configurable compu*ng resources that can be rapidly provisioned and released with minimal management effort or service provider interac*on. This cloud model is composed of five essen*al characteris*cs, three service models, and four deployment models» (*): Na+onal Ins+tute of Standards and Technology (NIST) 4

5 The emergence of the cloud has raised new issues and new security concerns. Cloud accessibility from everywhere exposes it to various types of web- based suck as the DDoS (distributed denial of service) A DDoS is an explicit to make a server, a service or a network unavailable to users by flooding the target request queue with fake requests. 5

6 Defini+on : «The degree to which a system is able to adapt to workload changes by provisioning and deprovisioning resources in an autonomic manner» Herbst and colleagues, According to the classificaqon of Galante and Bona, the elasqcity can be provided using three fundamental methods: 1. Horizontal scale; 2. VerQcal scale; 3. MigraQon. 6

7 Modeling and analyzing challenges: The lack of a generic and exhausqve methodology for modeling and analyzing cloud- based systems and their elasqcity. Solu+on: Formal methods a crucial step to reduce the modelling complexity and enhance the verificaqon of cloud- based systems and their elasqc behavior. à An approach based on bigraphical reacqve systems (BRS) for modeling the structure and behavior aspects of cloud systems and Maude language for the verificaqon of elasqcity property. 7

8 8

9 Graphical formalism for modelling, execuqng and analyzing ubiquitous compuqng systems. Meta- model which emphasizes both locality and connecqvity. 9

10 Formally a bigraph takes the form: G=(V, E, ctrl, G P, G L ) :I J V and E are respecqvely finite sets of nodes and edges ctrl=v K is a control map. G P =(V, ctrl, prnt):m n is the place graph. prnt :m V V n is a parent map. m is a finite ordinal number which represents sites. n is a finite ordinal number which represents regions. 10

11 Formally a bigraph takes the form: G=(V, E, ctrl, G P, G L ) :I J G L =(V, E, ctrl, link):x Y is the link graph. link :X P E Y is the link map. X,, Y are respecqvely sets of inner and outer names. P is a set of ports. I= m,x represents the inner face. J= n, Y represents the outer face. 11

12 Bigraphical ReacQve Systems consist of a category of bigraphs and a set of reacqon rules. ReacQon rules define the dynamics of bigraphs (NesQng and Linking). Defini+on : A reacqon rule (R, R, η) consists of a redex (R:m J) which may be transformed to a reactum (R : m J) to rewrite the bigraph where η: m m is map of ordinals. 12

13 13

14 Formal mapping based on correspondences between cloud system and BRS concepts. Cloud elements Cloud system Front- end, back- end Client, data center, load balancer, server, container, virtual machine, service Node idenqty InteracQon Abstract element ElasQcity acqon Cloud system structure Bigraphical concepts Bigraph CS =( V CS, E CS, ctrl CS, CS P, CS L ) Root: (0,1) Node: v V CS Control: k K CS Edge/Hyper edge: e i E CS Site: s i S CS Cloud system elas+c behavior ReacQon rule : CS R C S / R=(R, R,η) Each idenqfied cloud element h a s a precise semanqcs in the theory of BRS. Cloud system elasqc behavior is formally defined using reacqon rules. 14

15 Front- End/Back- End Addi+onal VM Nodes Loaded Server Open Link 15

16 Cloud- based systems elasqc behavior is expressed trough reacqon rules: CS R C S / R=(R, R,η). Each reacqon rule represent an elasqcity acqon which can be : triggered in response to workload changes, and applied in a specific cloud level (so_ware, pla`orm and infrastructure). This work focus only on modelling horizontal elasqcity and migraqon methods. AddiQonal reacqon rules are defined to express other behavioral situaqons (e.g. service allocaqon). 16

17 Cloud system Configura+on CS Reconfigura+on from CS to CS. Infrastructure Level Plaaorm Level BRS Bigraph: CS =( V CS, E CS, ctrl CS, CS P, CS L ) Meta- ReacQon rule: CS R C S / R=(R, R,η) Vm instance replica+on (horizontal scale) SE. VM.(S S L) d SE. VM.(S) VM.(S ) d Vm instance consolida+on (horizontal scale) SE. VM.(S) VM.(S ) d SE. VM.(S S ) d Virtual machine migra+on SE.(VM.(d) L d ) SE.(d ) SE.( d ) SE.(VM.(d) d ) Container instance replica+on (horizontal scale) SE. CN.(S S L) d SE. CN.(S) CN.(S ) d Container instance consolida+on (horizontal scale) SE. CN.(S) CN.(S ) d SE. CN.(S S ) d Container redeployment (migra+on) SE.(CN.(d) L d ) SE.(d ) SE.( d ) SE.(CN.(d) d ) Service instance replica+on (horizontal scale) Service Level SE.(VM. S d d ) SE.(VM. S S d d ) Service instance consolida+on (horizontal scale) SE.(VM. S S d d ) SE.(VM. S d d ) Service redeployment (migra+on) VM. S L d VM.(d ) VM.(d) VM.(S d ) 17

18 Virtual Machine Instance Replica+on Loaded Virtual Machine New Vm Instance Load Shared SE. VM.(S S L) d SE. VM.(S) VM.(S ) d 18

19 19

20 Tools built around BRS as BigMC (bigraphical model- checker) and DBtk are very limited and specific to some applicaqon domains. Maude language was used as alternaqve to overcome these different limits. Maude is a high- level formal specificaqon language based on equaqonal and rewriqng logics. It results on separately executable and verifiable specificaqons. 20

21 A projecqon from the BRS- based model of cloud systems to Maude language. The syntax of this Maude specificaqon is fully inspired from the bigraph term language. The specificaqon is composed of the following modules: specifica+on + simula+on (execu+on) 1. BiCLOUD_SYNTAX : The model s signature and semanqcs. 2. BiCLOUD_DYNAMIC: Behavioral aspects of the model through rewrite rules. 3. BiCLOUD_CHECK: states describing the elasqcity property (scale- up and scale- down states) verifica+on The proposed Maude- based approach is generic enough and may be easily extended. 21

22 Maude s search command and model- checking invariants technique are used in this work to verify the elasqcity property under finite reachability assumpqons. The syntax of the search command conforms to the following general scheme: search <Term- 1> <SearchArrow> <Term- 2> such that <Condi+on> Verifying the elasqcity property consists of checking that the cloud system is scaling up, when the workload rises and scaling down when it drops. In our case that means checking that the states (scale- up and scale- down) defined in the maude module BiCLOUD_CHECK are reachable from an iniqal state (<Term- 1>). Example : ConfiguraQon- Scenario1 =>* B:Bigraph such that elasqcity (B:Bigraph) == true 22

23 Ini+al State Reached States End of Search 23

24 24

25 Contribu+on: A formal modeling and verificaqon approach for cloud systems and their elasqcity based on bigraphical reacqve systems (BRS) and maude language. Ongoing research: Further refinements and extensions to our bigraphical model of systems to include addiqonal elasqcity aspects as the verqcal elasqcity. Apply our approach on large- scale cloud- based systems. Verify other proprieqes related to elasqc cloud- based systems. 25

26 Thank You For Your