Studied by 5 people
what is a distributed system?
a collection of loosely coupled nodes interconnected by a communication network
what is a site?
the location of a machine
what is a node?
a specific system (doesn't have to be a computer) at a site
nodes are called different names depending on context (eg. host/ machine/ site/ processor) - all mean a device connected with communication media
how does a specific node in a distributed system look and view resources?
its own resources are local the rest of the notes + their resources are remote
can a node vary in size?
yes, may vary in size and function eg. microprocessor vs. large general purpose computer system
what are the main principles of a distributed system?
one node at one site (eg. a server node) has a resource that a node at a different site (eg. a client/ user node) would like to use the network connects the sites and their resources
why do we need distributed systems?
resource sharing computation speedup reliability communication
what is resource sharing?
users at one site can use resources available at another site eg. site A and site B site A uses a printer at site B site B accesses a file store at site A
provides mechanisms for
sharing files at remote sites
processing information in a distributed database
printing files at remote sites
using remote specialized hardware devices (such as a supercomputer)
performing other operations
what is computation speedup?
some applications need lots of power and resources to compute
one computation can be divided into sub-computations and distributed across various sites.
computational speed-up is provided by running the subprocesses concurrently
allows for load sharing/ job migration - moving jobs from an overloaded site to another lightly loaded site (but commercial systems don’t usually have AUOTMATED load sharing)
what is reliability?
if one site fails then the remaining sites can continue operating making the system more reliable
for systems with many large autonomous machines, failure of one won’t affect the rest
for systems with few small machines where each machine does a crucial function, failure of one may halt the whole operation
with enough redundancy in hardware and data, the system could continue operating even if some sites have failed
how does the reliability benefit respond to site failure?
failure of site is detected by system and action needs to be taken to recover from the failure
system stops using the failed site resources
function of the failed site can be moved to another site and system needs to ensure transfer of function occurs correctly
when site is repaired system must use mechanisms to integrate back into the system correctly.
what is communication?
users at various sites can exchange information
low-level communication- eg. messages passed between systems
all high-level functionality of the standalone system can be expanded to encompass the distributed system and therefore functions can be carried out over larger distances
eg. file transfer, login, mail, remote procedure calls (RPCs)
how have the reasons for distributed systems impacted companies?
downsizing - companies replace big mainframes with distributed networks of workstations or personal computers. this provides the company with lots of advantages
what are the advantages of distributed systems?
reliability scalability flexibility speedup openness high performance
what is scalability?
scale up or down usage depending on if resources are needed or not needed, good because demand varies, using resources can be expensive
what is flexibility?
can run different operating systems
flexibility in locating resources and expanding facilities
what is openess?
more users can access resources without needing different installations or licencing
what are the disadvantages of distributed systems?
difficult troubleshooting less software support high network infrastructure cost security issues
what is difficult troubleshooting?
because different nodes communicate so more time and skill needed to pinpoint problem
what is less software support?
software may be in different areas so harder to support
what is security issues?
accessing remote resources can be taken advantaged of eg. DDoS attacks can be sent and spread
what is the organisation of distributed systems?
a layered architecture different sites connected by a distributed computing infrastructure (eg. cloud, grid) each site has a local OS distributed applications and middleware services span across all sites in the system
what are distributed applications?
applications that can run and communicate alongside applications on other sites, the user of the local node does not realise the app is being distributed
what are middleware services?
software acting like a hook to enable communication between different nodes
what is the distributed computing infrastructure?
the physical infrastructure that connects sites in a distributed system
what is the importance of layered architecture?
important because responsibility is divided (different responsibility for different layers) to support transparency, troubleshooting, updating networks complex and thus need to be organised
what is a layered architecure?
layers communicate and show an interface to other layers, so the layers know what information is sent or required but not what exactly is happening all layers + between layers have security measures common for all distributed systems
what are examples of distributed systems?
grid computing cloud computing - remote computers, virtualisation of hardware to use as cloud resources (VM to contribute resources) blockchain internet of things DDoS
all layered architectures
what is grid computing?
uses special software to enable several computers to work together on a common problem as if they were a massively parallel supercomputer (even when the machine not in use) nodes could be running software, data processing, connected to the grid
what are distributed simulations?
communicate to form a bigger simulation need to all be synchronised
what is cloud computing?
using a network of remote servers hosted on the Internet to store, manage, and process data, (virtualisation of hardware) rather than a local server or a personal computer.
what services does cloud computing offer?
SaaS - software as a service PaaS - platform as a service IaaS - infrastructure as a service
What is SaaS (Software As A Service)?
software that we don't install but lets us access other resources, eg. office 365 allows using word without downloading it
What is PaaS (Platform as a Service)?
platform to provide services that we need to access the resources example: Google app engine, Azure
What is IaaS (Infrastructure as a Service)?
the hardware used to provide the service
what are the different models of cloud computing
Private - eg. between company and employee cloud Community - for a government Public - accessible to all, eg. google Hybrid different model used depending on what security is required
what are the different resources for cloud computing?
Single/multi CPU, GPU, HPC, storage, etc
what are the different operating systems for cloud computing
eg. OpenStack, OpenNebula, Proprietary: used to create a cloud OS Virtualises hardware of services to create cloud resources for users
what is the cloudSME simulation platform?
API - can be an interface to let us access the services of another application
what is blockchain?
A decentralised architecture (peer to peer), digital ledger system for recording business transactions and events
what is a shared ledger?
a resource used by members in a network to record digital transactions each member stores an identical copy of the shared ledger changed to the ledger are reflected in all copies creating transparency and trust
what is the internet of things?
the idea that everything / every device could be given an ip address and put on the internet homogenous connected devices
What is a DDoS attack?
distributed denial of service attack - sending large amounts of traffic from multiple sources to a service or website, intending to overwhelm it so that authorised user are not able to access
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