What is a distributed system? - ANSWER it is a collection of autonomous
computing elements (either hardware devices or software processes) that appear
to the user as a single coherent system
Overlay network - ANSWER - used to organize a collection of nodes
- in this case, a node is a software process with a list of other processes it can
send messages to
What are some things that make coordination between nodes challenging? -
ANSWER - computing elements are autonomous and need to coordinate
- no global clock
- authenticating a node to identify group membership can create scalability
bottlenecks
What are the two ways to organize the collection of nodes for identifying which
nodes can communicate with one another? - ANSWER 1. Overlay network,
where the node has a list of other processes it can send messages to
2. A node may need to first look up a neighbour
distribution transparency - ANSWER the internal details of the distribution are
hidden from the user, this includes where the data is stored, on which computer
a process is executing, or how the data is replicated.
What challenge occurs when trying to create a single coherent system for a
distributed environment and distribution transparency? - ANSWER - partial
failures are inevitable and if the user is not aware of which node is failing or the
process that is failing on some set of unknown nodes then it will be hard to
debug
- with distribution transparency there is a performance price (say an application
repeatedly tries to contact a server before giving up, masking the server failure
before trying another one will slow down the system)
-there is also a trade-off with geographic scalability, since hiding latencies and
bandwidth restrictions are difficult
, - in some situations hiding distribution is not useful, like location based services
on mobile phones where you want to find the nearest store
Middleware for distributed systems offer what? - ANSWER - it is a manager
of resources that extends over multiple machines offering each application the
same interface
- it is a software layer placed between the OS and the distributed applications
it also offers:
- facilities for interapplication communication
- security services
- accounting services
- masking of and recovery from failures
- the main difference with the OS is that middleware is offered in a networked
env
What is a common communication service offered by middleware? - ANSWER
Remote Procedure Calls, which allow an application to invoke a function that is
implemented and executed on a remote computer as if it was locally available
4 Design goals of Distributed Systems - ANSWER - make resources easily
accessible and shareable
- hide that resources are distributed
- open
- scalable
Uniform Resource Locator (URL) - ANSWER - an address used for locating a
document on the Web.
- it gives no clue as to the location of the websites main web server
Mobile phone users can continue a conversation while they move, this is an
example of ________________________ - ANSWER migration transparency
To hide replication it is necessary that all replicas _____________ - ANSWER
- have the same name
- so the system also needs to support location transparency, otherwise it is
impossible to refer to replicas in diff locations
computing elements (either hardware devices or software processes) that appear
to the user as a single coherent system
Overlay network - ANSWER - used to organize a collection of nodes
- in this case, a node is a software process with a list of other processes it can
send messages to
What are some things that make coordination between nodes challenging? -
ANSWER - computing elements are autonomous and need to coordinate
- no global clock
- authenticating a node to identify group membership can create scalability
bottlenecks
What are the two ways to organize the collection of nodes for identifying which
nodes can communicate with one another? - ANSWER 1. Overlay network,
where the node has a list of other processes it can send messages to
2. A node may need to first look up a neighbour
distribution transparency - ANSWER the internal details of the distribution are
hidden from the user, this includes where the data is stored, on which computer
a process is executing, or how the data is replicated.
What challenge occurs when trying to create a single coherent system for a
distributed environment and distribution transparency? - ANSWER - partial
failures are inevitable and if the user is not aware of which node is failing or the
process that is failing on some set of unknown nodes then it will be hard to
debug
- with distribution transparency there is a performance price (say an application
repeatedly tries to contact a server before giving up, masking the server failure
before trying another one will slow down the system)
-there is also a trade-off with geographic scalability, since hiding latencies and
bandwidth restrictions are difficult
, - in some situations hiding distribution is not useful, like location based services
on mobile phones where you want to find the nearest store
Middleware for distributed systems offer what? - ANSWER - it is a manager
of resources that extends over multiple machines offering each application the
same interface
- it is a software layer placed between the OS and the distributed applications
it also offers:
- facilities for interapplication communication
- security services
- accounting services
- masking of and recovery from failures
- the main difference with the OS is that middleware is offered in a networked
env
What is a common communication service offered by middleware? - ANSWER
Remote Procedure Calls, which allow an application to invoke a function that is
implemented and executed on a remote computer as if it was locally available
4 Design goals of Distributed Systems - ANSWER - make resources easily
accessible and shareable
- hide that resources are distributed
- open
- scalable
Uniform Resource Locator (URL) - ANSWER - an address used for locating a
document on the Web.
- it gives no clue as to the location of the websites main web server
Mobile phone users can continue a conversation while they move, this is an
example of ________________________ - ANSWER migration transparency
To hide replication it is necessary that all replicas _____________ - ANSWER
- have the same name
- so the system also needs to support location transparency, otherwise it is
impossible to refer to replicas in diff locations
