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6.033 Spring 2018Lecture #1
• Complexity• Modularity and abstraction• Enforced modularity via client/server models
6.033 | spring 2018 | Katrina LaCurts 1
what is a system? a set of interconnected components that has an
expected behavior observed at the interface with its environment
what makes building systemsdifficult?
complexity
6.033 | spring 2018 | Katrina LaCurts 2
source: http://www.informationisbeautiful.net/visualizations/million-lines-of-code/
Today’s Systems are Incredibly Complex
© source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see https://ocw.mit.edu/help/faq-fair-use.
6.033 | spring 2018 | Katrina LaCurts 3
complexity limits what we can build and causes a number of unforeseen issues
6.033 | spring 2018 | Katrina LaCurts 4
how do we mitigate complexity?
with design principles such as modularity and abstraction
6.033 | spring 2018 | Katrina LaCurts 5
how do we enforce modularity?
one way is to use the client/server model
6.033 | spring 2018 | Katrina LaCurts 6
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Class Server(on machine 2) Class Browser
(on machine 1)
requestdef main(): def server_load_url(): html = browser_load_url(URL) ...
... return html
reply
6.033 | spring 2018 | Katrina LaCurts
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Stub Clients and RPCs Class Browser
(on machine 1)
def main(): def server_load_url(): html = browser_load_url(URL) ...
... return html
Class Server(on machine 2)
def browser_load_url(url): msg = url # could reformat send request wait for reply html = reply # could reformat
stub
return html
request
reply
def handle_server_load_url(url): wait for request url = request html = server_load_url(URL) reply = htmlsend reply stub
6.033 | spring 2018 | Katrina LaCurts
Challenges with RPCs
Client Server
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Challenges with RPCs
Client Serverinternet
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Challenges with RPCs
Client Serverinternet
load(“view.html?item”)
X
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Challenges with RPCs
Client Serverinternet
load(“view.html?item”)
Xload(“view.html?item”)
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Challenges with RPCs
Client Serverinternet
load(“buy.html?item&ccNo=xxx”)
X
6.033 | spring 2018 | Katrina LaCurts 13
Challenges with RPCs
Client Serverinternet
load(“buy.html?item&ccNo=xxx”)
Xload(“buy.html?item&ccNo=xxx”)
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Challenges with RPCs
Client Serverinternet
load(“buy.html?item&ccNo=xxx”)
Xload(“buy.html?item&ccNo=xxx”)
problem: just bought the same thing twice6.033 | spring 2018 | Katrina LaCurts
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Challenges with RPCs
Client Serverinternet
load(“buy.html?UID”)
Xload(“buy.html?UID”)
client | UID | reply
state on server
replay results from table instead of reprocessing
order
problem: server can still fail
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What else might we want?
Client Serverinternet
6.033 | spring 2018 | Katrina LaCurts 17
What else might we want?
Serverinternet
scalability
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What else might we want?
internet
scalability fault-tolerance/reliability
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What else might we want?
internet
scalability fault-tolerance/reliability
!
!!
6.033 | spring 2018 | Katrina LaCurts 20
What else might we want?
internet
scalability fault-tolerance/reliability
!
"
""
security
"
6.033 | spring 2018 | Katrina LaCurts 21
• Complexity limits what we can build, but can bemitigated with modularity and abstraction
• One way to enforce modularity is with a client/servermodel, where the two modules reside on differentmachines and communicate with RPCs; network/serverfailures are still an issue
next lecture: naming, which allows modules to communicate
coming up: operating systems, which enforce modularity on a single machine
6.033 | spring 2018 | Katrina LaCurts 22
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6.033 Computer System EngineeringSpring 2018
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