Questões de Concurso
Sobre interpretação de texto | reading comprehension em inglês
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There's lots of talk about network virtualization benefits, but are virtual network appliances all they're cracked up to be? Only in some scenarios.
Network virtualization benefits can be plentiful, but only in certain scenarios. Learn where virtual network appliances can work -- and where they can't.
If virtualization enables servers to be spun up and down on demand for cost efficiency and agility, wouldn't it make sense to implement virtual network components too? After all, virtual servers need to communicate inbound and outbound and still be firewall-protected and load balanced. That would seem to be best addressed by virtual network appliances that can be spun-up on demand, right? Only in some scenarios.
Many networking vendors have already begun to minimize development cost by using Intel-based platforms and commodity hardware. Examples of this range from the Cisco ASA firewall to F5 load balancers and Vyatta routers. The obvious next step for some of these vendors has been to offer their products in virtual appliance packaging. F5 took a small step forward with the Local Traffic Manager - Virtual Edition (LTM VE), while Vyatta claims to offer a full range of virtual appliance solutions. VMware was somewhat late to the game, but it also offers virtualized firewalls (vShield Zones and vShield App) and routers/load balancers (vShield Edge).
Virtual network appliances: What's the catch?
The problem is that unlike servers, networking appliances commonly perform I/O-intensive tasks, moving large amounts of data between network interfaces with minimal additional processing, relying heavily on dedicated hardware. All high-speed routing and packet forwarding, as well as encryption (both IPsec and SSL) and load balancing, rely on dedicated silicon. When a networking appliance is repackaged into a virtual machine format, the dedicated hardware is gone, and all these tasks must now be performed by the general- purpose CPU, sometimes resulting in extreme reduction in performance.
Implementing routers, switches or firewalls in a virtual appliance would just burn the CPU cycles that could be better used elsewhere -- unless, of course, you’ve over-provisioned your servers and have plenty of idle CPU cycles, in which case something has gone seriously wrong with your planning.
To make matters worse, the hypervisor software used in server virtualization solutions also virtualizes the network interfaces. That means that every I/O access path to virtualized hardware from the networking appliance results in a context switch to higher privilege software (the hypervisor), which uses numerous CPU cycles to decode what needs to be done and emulate the desired action. Also, data passed between virtual machines must be copied between their address spaces, adding further latency to the process.
There is some help in that the VMware hypervisor has the DVFilter API, which allows a loadable kernel module to inspect and modify network traffic either within the hypervisor (vNetwork Data Path Agent) or in combination with a virtual machine (vNetwork Control Path Agent). The loadable kernel module significantly reduces the VM context switching overhead.
Where virtual network appliances can work?
There are some use cases in which virtual network appliances make perfect sense. For instance, you could virtualize an appliance that performs lots of CPU-intensive processing with no reliance on dedicated hardware. Web application firewalls (WAFs) and complex load balancers are perfect examples (no wonder they’re commonly implemented as loadable modules in Apache Web servers or as Squid reverse proxy servers).
Also, if you’re planning to roll out multi-tenant cloud, the flexibility gained by treating networking appliances as click-to-deploy Lego bricks might more than justify the subpar performance. This is especially so if you charge your users by their actual VM/CPU usage, in which case you don’t really care how much CPU they’re using.
Virtualized networking also makes sense when firewall and routing functions are implemented as part of the virtual switch in each hypervisor. This could result in optimal traffic flow between virtual machines (regardless of whether they belong to the same IP subnet or not) and solve the problem of traffic trombones. Unfortunately, it seems that Cisco is still the only vendor that extends the VMware hypervisor switch using the Virtual Ethernet Module (VEM) functionality. While numerous security solutions already deploy the VMsafe APIs, the networking appliances I’ve seen so far (including the vShield Edge from VMware) rely on virtual machines to forward traffic between virtual (or physical) LANs.
Obviously the networking vendors have a very long way to go before reaching the true potential of virtualized networking.
Disponível em: http://searchnetworking.techtarget.com/tip/Virtual-network-appliances-Benefits-and- drawbacks
Search Networking - Tech Target - Texto de Ivan Pepelnjak (Março de 2011)
There's lots of talk about network virtualization benefits, but are virtual network appliances all they're cracked up to be? Only in some scenarios.
Network virtualization benefits can be plentiful, but only in certain scenarios. Learn where virtual network appliances can work -- and where they can't.
If virtualization enables servers to be spun up and down on demand for cost efficiency and agility, wouldn't it make sense to implement virtual network components too? After all, virtual servers need to communicate inbound and outbound and still be firewall-protected and load balanced. That would seem to be best addressed by virtual network appliances that can be spun-up on demand, right? Only in some scenarios.
Many networking vendors have already begun to minimize development cost by using Intel-based platforms and commodity hardware. Examples of this range from the Cisco ASA firewall to F5 load balancers and Vyatta routers. The obvious next step for some of these vendors has been to offer their products in virtual appliance packaging. F5 took a small step forward with the Local Traffic Manager - Virtual Edition (LTM VE), while Vyatta claims to offer a full range of virtual appliance solutions. VMware was somewhat late to the game, but it also offers virtualized firewalls (vShield Zones and vShield App) and routers/load balancers (vShield Edge).
Virtual network appliances: What's the catch?
The problem is that unlike servers, networking appliances commonly perform I/O-intensive tasks, moving large amounts of data between network interfaces with minimal additional processing, relying heavily on dedicated hardware. All high-speed routing and packet forwarding, as well as encryption (both IPsec and SSL) and load balancing, rely on dedicated silicon. When a networking appliance is repackaged into a virtual machine format, the dedicated hardware is gone, and all these tasks must now be performed by the general- purpose CPU, sometimes resulting in extreme reduction in performance.
Implementing routers, switches or firewalls in a virtual appliance would just burn the CPU cycles that could be better used elsewhere -- unless, of course, you’ve over-provisioned your servers and have plenty of idle CPU cycles, in which case something has gone seriously wrong with your planning.
To make matters worse, the hypervisor software used in server virtualization solutions also virtualizes the network interfaces. That means that every I/O access path to virtualized hardware from the networking appliance results in a context switch to higher privilege software (the hypervisor), which uses numerous CPU cycles to decode what needs to be done and emulate the desired action. Also, data passed between virtual machines must be copied between their address spaces, adding further latency to the process.
There is some help in that the VMware hypervisor has the DVFilter API, which allows a loadable kernel module to inspect and modify network traffic either within the hypervisor (vNetwork Data Path Agent) or in combination with a virtual machine (vNetwork Control Path Agent). The loadable kernel module significantly reduces the VM context switching overhead.
Where virtual network appliances can work?
There are some use cases in which virtual network appliances make perfect sense. For instance, you could virtualize an appliance that performs lots of CPU-intensive processing with no reliance on dedicated hardware. Web application firewalls (WAFs) and complex load balancers are perfect examples (no wonder they’re commonly implemented as loadable modules in Apache Web servers or as Squid reverse proxy servers).
Also, if you’re planning to roll out multi-tenant cloud, the flexibility gained by treating networking appliances as click-to-deploy Lego bricks might more than justify the subpar performance. This is especially so if you charge your users by their actual VM/CPU usage, in which case you don’t really care how much CPU they’re using.
Virtualized networking also makes sense when firewall and routing functions are implemented as part of the virtual switch in each hypervisor. This could result in optimal traffic flow between virtual machines (regardless of whether they belong to the same IP subnet or not) and solve the problem of traffic trombones. Unfortunately, it seems that Cisco is still the only vendor that extends the VMware hypervisor switch using the Virtual Ethernet Module (VEM) functionality. While numerous security solutions already deploy the VMsafe APIs, the networking appliances I’ve seen so far (including the vShield Edge from VMware) rely on virtual machines to forward traffic between virtual (or physical) LANs.
Obviously the networking vendors have a very long way to go before reaching the true potential of virtualized networking.
Disponível em: http://searchnetworking.techtarget.com/tip/Virtual-network-appliances-Benefits-and- drawbacks
Search Networking - Tech Target - Texto de Ivan Pepelnjak (Março de 2011)
O requisito de hardware necessário e o desempenho esperado das aplicações são, respectivamente:
There's lots of talk about network virtualization benefits, but are virtual network appliances all they're cracked up to be? Only in some scenarios.
Network virtualization benefits can be plentiful, but only in certain scenarios. Learn where virtual network appliances can work -- and where they can't.
If virtualization enables servers to be spun up and down on demand for cost efficiency and agility, wouldn't it make sense to implement virtual network components too? After all, virtual servers need to communicate inbound and outbound and still be firewall-protected and load balanced. That would seem to be best addressed by virtual network appliances that can be spun-up on demand, right? Only in some scenarios.
Many networking vendors have already begun to minimize development cost by using Intel-based platforms and commodity hardware. Examples of this range from the Cisco ASA firewall to F5 load balancers and Vyatta routers. The obvious next step for some of these vendors has been to offer their products in virtual appliance packaging. F5 took a small step forward with the Local Traffic Manager - Virtual Edition (LTM VE), while Vyatta claims to offer a full range of virtual appliance solutions. VMware was somewhat late to the game, but it also offers virtualized firewalls (vShield Zones and vShield App) and routers/load balancers (vShield Edge).
Virtual network appliances: What's the catch?
The problem is that unlike servers, networking appliances commonly perform I/O-intensive tasks, moving large amounts of data between network interfaces with minimal additional processing, relying heavily on dedicated hardware. All high-speed routing and packet forwarding, as well as encryption (both IPsec and SSL) and load balancing, rely on dedicated silicon. When a networking appliance is repackaged into a virtual machine format, the dedicated hardware is gone, and all these tasks must now be performed by the general- purpose CPU, sometimes resulting in extreme reduction in performance.
Implementing routers, switches or firewalls in a virtual appliance would just burn the CPU cycles that could be better used elsewhere -- unless, of course, you’ve over-provisioned your servers and have plenty of idle CPU cycles, in which case something has gone seriously wrong with your planning.
To make matters worse, the hypervisor software used in server virtualization solutions also virtualizes the network interfaces. That means that every I/O access path to virtualized hardware from the networking appliance results in a context switch to higher privilege software (the hypervisor), which uses numerous CPU cycles to decode what needs to be done and emulate the desired action. Also, data passed between virtual machines must be copied between their address spaces, adding further latency to the process.
There is some help in that the VMware hypervisor has the DVFilter API, which allows a loadable kernel module to inspect and modify network traffic either within the hypervisor (vNetwork Data Path Agent) or in combination with a virtual machine (vNetwork Control Path Agent). The loadable kernel module significantly reduces the VM context switching overhead.
Where virtual network appliances can work?
There are some use cases in which virtual network appliances make perfect sense. For instance, you could virtualize an appliance that performs lots of CPU-intensive processing with no reliance on dedicated hardware. Web application firewalls (WAFs) and complex load balancers are perfect examples (no wonder they’re commonly implemented as loadable modules in Apache Web servers or as Squid reverse proxy servers).
Also, if you’re planning to roll out multi-tenant cloud, the flexibility gained by treating networking appliances as click-to-deploy Lego bricks might more than justify the subpar performance. This is especially so if you charge your users by their actual VM/CPU usage, in which case you don’t really care how much CPU they’re using.
Virtualized networking also makes sense when firewall and routing functions are implemented as part of the virtual switch in each hypervisor. This could result in optimal traffic flow between virtual machines (regardless of whether they belong to the same IP subnet or not) and solve the problem of traffic trombones. Unfortunately, it seems that Cisco is still the only vendor that extends the VMware hypervisor switch using the Virtual Ethernet Module (VEM) functionality. While numerous security solutions already deploy the VMsafe APIs, the networking appliances I’ve seen so far (including the vShield Edge from VMware) rely on virtual machines to forward traffic between virtual (or physical) LANs.
Obviously the networking vendors have a very long way to go before reaching the true potential of virtualized networking.
Disponível em: http://searchnetworking.techtarget.com/tip/Virtual-network-appliances-Benefits-and- drawbacks
Search Networking - Tech Target - Texto de Ivan Pepelnjak (Março de 2011)
Barack Obama just became the first US president to write a line of computer code (assuming George W. Bush never secretly indulged in PHP). At the White House yesterday, Obama sat down with students who were learning the fundamentals of JavaScript, the popular programming language used to create most web pages.
The line he wrote was:
moveForward(100);
“So I make the F in higher case?” Obama asked, correctly observing that JavaScript is case sensitive. “Semicolon?” (That semicolon is optional, but Obama apparently has a knack for recognizing JavaScript best practices.)
Obama was playing with a Code.org tutorial based on the popular Disney movie Frozen. In his line of code, the President called a function-moveForward-pre-defined by Code.org for the exercise.
Calling a function in JavaScript is simple: write its name exactly as it has been defined, followed by parentheses that contain its “arguments.” In this case, a single argument tells the program how many pixels to move a Frozen character forward. Because it’s measured in pixels, the argument has to be a number. If Obama had written moveForward(“three steps”), the program would have failed, offering only a cryptic error message and exposing the president to the near-perpetual state of frustration most software developers live in.
“This is Elsa?” Obama asked, referring to the movie’s main character.
Obama was promoting Computer Science Education Week and Code.org’s Hour of Code campaign, which encourages kids to try programming for at least one hour. “It turns out the concepts are not that complicated,” Obama told the students at the White House, though his attempt to explain it suggested otherwise:
“The basic concept behind coding is that you take zeros and ones, you take two numbers, yes or no, and those can be translated into electrical messages that then run through the computer…. So all it’s doing is it’s saying yes or no over and over again, and the computer’s powerful enough that it can read a really long set of instructions really quickly.”
Something like that.
Disponível em: http://qz.com/308904/heres-the-first-line-of-code-ever-written-by-a-us-president/
Quartz (9 de Dezembro de 2014) - Texto de Zachary M. Seward
Barack Obama just became the first US president to write a line of computer code (assuming George W. Bush never secretly indulged in PHP). At the White House yesterday, Obama sat down with students who were learning the fundamentals of JavaScript, the popular programming language used to create most web pages.
The line he wrote was:
moveForward(100);
“So I make the F in higher case?” Obama asked, correctly observing that JavaScript is case sensitive. “Semicolon?” (That semicolon is optional, but Obama apparently has a knack for recognizing JavaScript best practices.)
Obama was playing with a Code.org tutorial based on the popular Disney movie Frozen. In his line of code, the President called a function-moveForward-pre-defined by Code.org for the exercise.
Calling a function in JavaScript is simple: write its name exactly as it has been defined, followed by parentheses that contain its “arguments.” In this case, a single argument tells the program how many pixels to move a Frozen character forward. Because it’s measured in pixels, the argument has to be a number. If Obama had written moveForward(“three steps”), the program would have failed, offering only a cryptic error message and exposing the president to the near-perpetual state of frustration most software developers live in.
“This is Elsa?” Obama asked, referring to the movie’s main character.
Obama was promoting Computer Science Education Week and Code.org’s Hour of Code campaign, which encourages kids to try programming for at least one hour. “It turns out the concepts are not that complicated,” Obama told the students at the White House, though his attempt to explain it suggested otherwise:
“The basic concept behind coding is that you take zeros and ones, you take two numbers, yes or no, and those can be translated into electrical messages that then run through the computer…. So all it’s doing is it’s saying yes or no over and over again, and the computer’s powerful enough that it can read a really long set of instructions really quickly.”
Something like that.
Disponível em: http://qz.com/308904/heres-the-first-line-of-code-ever-written-by-a-us-president/
Quartz (9 de Dezembro de 2014) - Texto de Zachary M. Seward
Barack Obama just became the first US president to write a line of computer code (assuming George W. Bush never secretly indulged in PHP). At the White House yesterday, Obama sat down with students who were learning the fundamentals of JavaScript, the popular programming language used to create most web pages.
The line he wrote was:
moveForward(100);
“So I make the F in higher case?” Obama asked, correctly observing that JavaScript is case sensitive. “Semicolon?” (That semicolon is optional, but Obama apparently has a knack for recognizing JavaScript best practices.)
Obama was playing with a Code.org tutorial based on the popular Disney movie Frozen. In his line of code, the President called a function-moveForward-pre-defined by Code.org for the exercise.
Calling a function in JavaScript is simple: write its name exactly as it has been defined, followed by parentheses that contain its “arguments.” In this case, a single argument tells the program how many pixels to move a Frozen character forward. Because it’s measured in pixels, the argument has to be a number. If Obama had written moveForward(“three steps”), the program would have failed, offering only a cryptic error message and exposing the president to the near-perpetual state of frustration most software developers live in.
“This is Elsa?” Obama asked, referring to the movie’s main character.
Obama was promoting Computer Science Education Week and Code.org’s Hour of Code campaign, which encourages kids to try programming for at least one hour. “It turns out the concepts are not that complicated,” Obama told the students at the White House, though his attempt to explain it suggested otherwise:
“The basic concept behind coding is that you take zeros and ones, you take two numbers, yes or no, and those can be translated into electrical messages that then run through the computer…. So all it’s doing is it’s saying yes or no over and over again, and the computer’s powerful enough that it can read a really long set of instructions really quickly.”
Something like that.
Disponível em: http://qz.com/308904/heres-the-first-line-of-code-ever-written-by-a-us-president/
Quartz (9 de Dezembro de 2014) - Texto de Zachary M. Seward
This is not a great time to be a recent college graduate.
Average student-loan debt is $29,400. The underemployment rate is 44 percent for graduates ages 22 to 27, meaning they are holding jobs that don’t require bachelor’s degrees. And the average age of financial independence for college graduate these days is 30.
Such statistics have given rise to the narrative that a college degree is no longer worth it, although volumes of economic studies on lifetime earnings prove otherwise. Even so, given the number of college graduates struggling to launch their careers, a wide gap has emerged between what the workforce needs in employees and what colleges are producing in graduates.
Part of the problem is that we have high expectations for the bachelor’s degree today. Thirty years ago, when fewer people required a higher education to get ahead in life, the bachelor’s degree was seen as a vehicle for broad learning. The training part came later by going to graduate school or getting a job where the new employer trained you.
Now we demand that skills training move in tandem with broad learning, and expect both to be completed in the four years of an undergraduate education. For too many students, however, the bachelor’s degree is not providing that dual experience - high-impact, in-classroom learning and out-of-the- classroom, experiential, and hands-on learning necessary for success in today’s economy.
Because of student loan debt, graduate or professional school is no longer an option for many recent college graduates. They’re searching for quick and cheap add- on boot camps that give them what they’re missing. And a whole new set of providers are emerging outside of the traditional higher-education ecosystem to provide that lift.
Last year, General Assembly, which offers courses of a few hours to a few weeks in everything from digital marketing to web development, expanded to Washington, DC, where it is selling out of nearly all of its offerings. Its average student is in his mid-20s and just a few years out of college.
I. colleges are not producing in graduates what the workforce needs in employees.
II. nowadays, the bachelor’s degree is seen only as a vehicle for broad learning.
III. nearly 44% of graduates ages 22 to 27 hold jobs that require bachelor’s degree.
IV. colleges are expected to give students not only skills training, but also broad learning.
V. economic studies on lifetime earnings prove a college degree is no longer worth it.
The correct assumption(s) is(are)
The 2014 World Cup has seen innovations such as goal-line technology and vanishing spray introduced to football’s showpiece global event for the first time.
France benefited from the use of goal-line technology in their opening win over Honduras.
With language barriers no longer a problem, red and yellow cards were introduced at the 1970 World Cup and have been adopted worldwide since, with variants appearing in many other sports.
Cats are at a crucial point in their evolutionary journey as they transform from solitary hunters to domestic pets, a study by the BBC and the Royal Veterinary College has revealed.
Cats see the world in muted colours, making it easier for them to see movement without distractions. They also have large eyes for their size, allowing them to see well in low-level light.
However, they can’t focus on anything less than a foot away, so use their whiskers for detecting objects closer to their bodies.
“The team believes the impact has left behind a 40m- wide crater.
‘That’s the estimation we have made according to current impact models. We expect that soon Nasa could observe the crater and confirm our prediction,’ said Prof Madiedo.
It would be one of many scars on the lunar surface. Unlike Earth, the Moon has no atmosphere to shield it from meteorite collisions, and its surface shows a record of every strike.”
Nos dois últimos versos da canção – “And I swear that I don’t have a gun / No I don’t have a gun”–, o
autor lamenta o fato de não possuir uma arma.
O autor dessa canção dirige-se às pessoas em geral, enfatizando que elas se apresentem e sejam aceitas como realmente são, sem quaisquer restrições.