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A look at Twitch’s live video streaming infrastructure

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A look at Twitch’s live video streaming infrastructure

Twitch engineering created a scalable, HA streaming solution that would allow broadcasters to live stream their games with minimal latency.

The live streaming solution (developed by Twitch) is also made available as a Service to the world through AWS IVS (Interactive Video Streaming) that would enable other businesses leveraging AWS to integrate interactive streaming services with their apps or websites.

AWS IS a fully managed live streaming service that handles all aspects of live streaming, including transcoding, packaging and delivery to end viewers.

AWS IVS

Key points from the Twitch infrastructure:

They have hundreds of thousands of concurrent live broadcasters on their platform. Five quality levels are available to adjust to viewers’ network conditions.

The stream has a buffer that allows the viewer to download the video to their device in advance to ensure smooth streaming.

Over the years, Twitch has managed to reduce the streaming latency from 15 to 3 seconds. The latency drops to 1.5 seconds under the best network conditions. This is, for example, when it happens in Korea.

Why is latency important for live steams? Can the video be buffered so that it can be played as a normal video?

The shorter the time between when a streamer waves at a camera and when viewers see the wave, the better the user experience on this platform. A lower latency allows for more interaction between streamers and viewers.

When a streamer begins their stream, Twitch servers transcode their video. Transcoding is a system written in C/C++, Go and converts the stream to multiple formats that can be played on the viewer’s device under different network conditions. Transcoded formats are distributed to multiple data centers and PoPs (Point of Presence) worldwide. This ensures that viewers’ location is within easy reach.

Transcoding can be computationally costly. Twitch initially transcoded just two to three percent. They have since reduced the cost of their hardware-based transcoder, which allows them to transcode every video uploaded to their servers.

Twitch live video streaming
Img Src: Twitch engineering

Speaking of the physical infrastructure, to ensure smooth streaming, they’ve partnered up with the local ISPs and have several PoPs (Point of Presence) powered by the backbone network that connects them with the data centers.

If you wish to understand PoPs, and other cloud fundamentals in-depth, including how cloud infrastructure deploys and scales our apps globally and more, check out my platform-agnostic Cloud Computing 101 course.

Viewers around the globe can download the videos from PoPs. The intelligent network ensures that streams are replicated on Twitch in close proximity to their viewers. It would be impossible to replicate all channels on their network.

Replication of data is done based on a metric called reach, which determines the percentage of people with a certain quality of internet access and the quality of streaming they would get from the platform. Although the approach isn’t very precise, it gives Twitch a high-level overview that allows them to design their infrastructure to maximize quality and reduce deployment costs.

Live video streams are sent to the PoPs for processing and distribution throughout the Twitch network. Origin data centers handle computation-intensive processes like video transcoding. Twitch began with one origin data center that processed live streams. The PoPs ran HAProxy and routed the streams to the origin data center. The HAProxy approach presented some challenges as the platform gained popularity and increased the number of data center.

The HAProxy configuration meant that only one of the origin data center’s PoPs could receive live video streams. This resulted in inefficient use of infrastructure resources.

It got difficult to handle the unexpected traffic surge during key online events.

PoPs could not detect overloaded or defective origin data centers, and sent traffic their way instead of routing it to other data centres.

In order to deal with these challenges, they retired HAProxy and developed Intelligest–an ingest routing system to intelligently distribute live video traffic from the PoPs to the origins. The Intelligest architecture is made up of two components. There’s an Intelligest Media Proxy running in every PoP, and an Intelligest Routing Service running in AWS.

The IRS assists the media proxy in determining the correct origin data center to send traffic to. This overcomes the difficulties faced by HAProxy.

IRS has further two sub-services, the Capacitor and the Well. The Capacitor monitors compute resources in each origin data center, while the Well monitors backbone network bandwidth availability. IRS can use these to determine the infrastructure capacity in real time. Twitch has been able to achieve high availability of their infrastructure. If you found this content interesting, please consider signing up for my newsletter to receive the most recent content directly to your inbox.

Information source: Twitch engineering

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For a complete list of similar articles on distributed systems and real-world architectures here you go

Handpicked Resources to Learn Software Architecture and Large Scale Distributed Systems Design

I’ve put together a list of resources (online courses + books) that I believe are super helpful in building a solid foundation in software architecture and designing large-scale distributed systems like Facebook, YouTube, Gmail, Uber, and so on. You can check it out.

Share the article on the internet if you enjoyed it. Follow scaleyourapp.com via social media (links below) to be notified when new content is published. I am Shivang, you can read about me here!

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Google Pixel 7 and 7 Pro are getting a built-in VPN at no extra cost

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Google Pixel 7 and 7 Pro are getting a built-in VPN at no extra cost
Google Pixel 7 Pro hands on front Snow



(Image credit: Future / Lance Ulanoff)

Users of the Google Pixel 7 and 7 Pro devices will be able to secure their data without the need to pay for an additional Android VPN after the company said it would be including its Google One VPN service at no extra cost. 

The move will make the Pixel 7 and 7 Pro the first smartphones to include a free VPN connection. 

The offer is restricted to just some countries, though – and what’s more, some data won’t be secured inside the VPN tunnel.  

Peace of mind when you connect online ✨Later this year, #Pixel7 and 7 Pro will be the only phones with a VPN by Google One—at no extra cost.¹#MadeByGoogle¹See image for more info pic.twitter.com/P7lzyoMdekOctober 6, 2022

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Google Pixel 7 VPN

Despite the aforementioned limits, the big tech giant assures that the VPN software won’t associate users’ app and browsing data with users’ accounts. 

Google One VPN typically costs around $10 per month as part of the company’s Premium One plan, which also comes with a 2TB of cloud storage on top. 

This decision is the latest move to bring Google’s mobile data security to the next level. Not too long ago, the company made Google One VPN available also for iOS devices, and also introduced the option of having an always-on VPN across its latest smartphones. 

Google promises that its secure VPN software will shield your phone against hackers on unsecure networks, like public Wi-Fi. It will also hide your IP address so that third parties won’t be able to track your location.

Shorter for virtual private network, a VPN is exactly the tool you want to shield your sensitive data as it masks your real location and encrypts all your data in transit. Beside privacy, it can allow you to bypass geo-restrictions and other online blocks. 

Chiara is a multimedia journalist, with a special eye for latest trends and issues in cybersecurity. She is a Staff Writer at Future with a focus on VPNs. She mainly writes news and features about data privacy, online censorship and digital rights for TechRadar, Tom’s Guide and T3. With a passion for digital storytelling in all its forms, she also loves photography, video making and podcasting. Originally from Milan in Italy, she is now based in Bristol, UK, since 2018.

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The Steam Deck dock is finally here and will ship faster than you think

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The Steam Deck dock is finally here and will ship faster than you think
a steam deck placed in a steam deck dock



(Image credit: Valve)

After months of waiting and delays, Valve has finally announced that the Steam Deck dock is available for purchase on its official site.

Not only that but, according to Valve, the dock will ship out in an incredibly fast one to two weeks, which pairs with the fact that the Steam Deck itself is now shipping with no wait time (not to mention that it’s incredibly easy to set up). The port selection is pretty solid as well, with the dock featuring three USB-A 3.1 gen 1 ports, one Ethernet port, a DisplayPort 1.4, and an HDMI 2.0 port. And for its power supply, it uses a USB-C passthrough delivery.

A Steam Deck dock will run you $90 (around £81 / AU$140), which is a bit steeper than most third-party options on the market right now. But for those waiting it out for an official product until now, price most likely will not be an issue.

Is it worth buying? 

Considering that even Steam Decks themselves are shipping without a queue and that the dock has such a quick turnaround to delivery, it seems that the supply chain issues that had been gripping Valve are loosening considerably.

However, the deck itself is far from perfect. Because of the fact that it uses USB-C for the display port, a third-party USB-C dock that uses its own power supply and video out will output the display of the official dock. 

And as mentioned before, the price of the official Steam Deck dock is steeper than many third-party options on the market, meaning that those who are on a budget might pass this product up in favor of a lower-priced one.

There are also some bugs that Valve is working on fixing at this time, including one involving compatibility with LG displays. According to the FAQ, if the “Docking Station is connected via HDMI, sleep/wake can result in visual noise.”

It might be worth waiting for Valve to work out the kinks of its dock before investing in one. And while you’re waiting, research other options that might better suit your needs.

Allisa has been freelancing at TechRadar for nine months before joining as a Computing Staff Writer. She mainly covers breaking news and rumors in the computing industry, and does reviews and featured articles for the site. In her spare time you can find her chatting it up on her two podcasts, Megaten Marathon and Combo Chain, as well as playing any JRPGs she can get her hands on.

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Why doesn’t Bash’s `set -e` do what I expected?

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Why doesn’t set -e (or set -o errexit, or trap ERR) do what I expected?

set -e was an attempt to add “automatic error detection” to the shell. Its goal was to cause the shell to abort any time an error occurred, so you don’t have to put || exit 1 after each important command. This does not work well in practice.

The goal of automatic error detection is a noble one, but it requires the ability to tell when an error actually occurred. In modern high-level languages, most tasks are performed by using the language’s builtin commands or features. The language knows whether (for example) you tried to divide by zero, or open a file that you can’t open, and so on. It can take action based on this knowledge.

But in the shell, most of the tasks you actually care about are done by external programs. The shell can’t tell whether an external program encountered something that it considers an error — and even if it could, it wouldn’t know whether the error is an important one, worthy of aborting the entire program, or whether it should carry on.

The only information conveyed to the shell by the external program is an exit status — by convention, 0 for success, and non-zero for “some kind of error”. The developers of the original Bourne shell decided that they would create a feature that would allow the shell to check the exit status of every command that it runs, and abort if one of them returns non-zero. Thus, set -e was born.

But many commands return non-zero even when there wasn’t an error. For example,

if [ -d /foo ]; then ...; else ...; fi

If the directory doesn’t exist, the [ command returns non-zero. Clearly we don’t want to abort when that happens — our script wants to handle that in the else part. So the shell implementors made a bunch of special rules, like “commands that are part of an if test are immune”, and “commands in a pipeline, other than the last one, are immune”.

These rules are extremely convoluted, and they still fail to catch even some remarkably simple cases. Even worse, the rules change from one Bash version to another, as Bash attempts to track the extremely slippery POSIX definition of this “feature”. When a SubShell is involved, it gets worse still — the behavior changes depending on whether Bash is invoked in POSIX mode. Another wiki has a page that covers this in more detail. Be sure to check the caveats.

A reference comparing behavior across various historical shells also exists.

Story time

Consider this allegory, originally posted to bug-bash:

Once upon a time, a man with a dirty lab coat and long, uncombed hair
showed up at the town police station, demanding to see the chief of
police.  "I've done it!" he exclaimed.  "I've built the perfect
criminal-catching robot!"

The police chief was skeptical, but decided that it might be worth
the time to see what the man had invented.  Also, he secretly thought,
it might be a somewhat unwise move to completely alienate the mad
scientist and his army of hunter robots.

So, the man explained to the police chief how his invention could tell
the difference between a criminal and law-abiding citizen using a
series of heuristics.  "It's especially good at spotting recently
escaped prisoners!" he said.  "Guaranteed non-lethal restraints!"

Frowning and increasingly skeptical, the police chief nevertheless
allowed the man to demonstrate one robot for a week.  They decided that
the robot should patrol around the jail.  Sure enough, there was a
jailbreak a few days later, and an inmate digging up through the
ground outside of the prison facility was grabbed by the robot and
carried back inside the prison.

The surprised police chief allowed the robot to patrol a wider area.
The next day, the chief received an angry call from the zookeeper.
It seems the robot had cut through the bars of one of the animal cages,
grabbed the animal, and delivered it to the prison.

The chief confronted the robot's inventor, who asked what animal it
was.  "A zebra," replied the police chief.  The man slapped his head and
exclaimed, "Curses!  It was fooled by the black and white stripes!
I shall have to recalibrate!"  And so the man set about rewriting the
robot's code.  Black and white stripes would indicate an escaped
inmate UNLESS the inmate had more than two legs.  Then it should be
left alone.

The robot was redeployed with the updated code, and seemed to be
operating well enough for a few days.  Then on Saturday, a mob of
children in soccer clothing, followed by their parents, descended
on the police station.  After the chaos subsided, the chief was told
that the robot had absconded with the referee right in the middle of
a soccer game.

Scowling, the chief reported this to the scientist, who performed a
second calibration.  Black and white stripes would indicate an escaped
inmate UNLESS the inmate had more than two legs OR had a whistle on
a necklace.

Despite the second calibration, the police chief declared that the robot
would no longer be allowed to operate in his town.  However, the news
of the robot had spread, and requests from many larger cities were
pouring in.  The inventor made dozens more robots, and shipped them off
to eager police stations around the nation.  Every time a robot grabbed
something that wasn't an escaped inmate, the scientist was consulted,
and the robot was recalibrated.

Unfortunately, the inventor was just one man, and he didn't have the
time or the resources to recalibrate EVERY robot whenever one of them
went awry.  The robot in Shangri-La was recalibrated not to grab a
grave-digger working on a cold winter night while wearing a ski mask,
and the robot in Xanadu was recalibrated not to capture a black and
white television set that showed a movie about a prison break, and so
on.  But the robot in Xanadu would still grab grave-diggers with ski
masks (which it turns out was not common due to Xanadu's warmer climate),
and the robot in Shangri-La was still a menace to old televisions (of
which there were very few, the people of Shangri-La being on the average
more wealthy than those of Xanadu).

So, after a few years, there were different revisions of the
criminal-catching robot in most of the major cities.  In some places,
a clever criminal could avoid capture by wearing a whistle on a string
around the neck.  In others, one would be well-advised not to wear orange
clothing in certain rural areas, no matter how close to the Harvest
Festival it was, unless one also wore the traditional black triangular
eye-paint of the Pumpkin King.

Many people thought, "This is lunacy!"  But others thought the robots
did more good than harm, all things considered, and so in some places
the robots are used, while in other places they are shunned.

The end.

Exercises

Or, “so you think set -e is OK, huh?”

Exercise 1: why doesn’t this example print anything?

   1 
   2 set -e
   3 i=0
   4 let i++
   5 echo "i is $i"

Exercise 2: why does this one sometimes appear to work? In which versions of bash does it work, and in which versions does it fail?

   1 
   2 set -e
   3 i=0
   4 ((i++))
   5 echo "i is $i"

Exercise 3: why aren’t these two scripts identical?

   1 
   2 set -e
   3 test -d nosuchdir && echo no dir
   4 echo survived
   1 
   2 set -e
   3 f() { test -d nosuchdir && echo no dir; }
   4 f
   5 echo survived

Exercise 4: why aren’t these two scripts identical?

   1 set -e
   2 f() { test -d nosuchdir && echo no dir; }
   3 f
   4 echo survived
   1 set -e
   2 f() { if test -d nosuchdir; then echo no dir; fi; }
   3 f
   4 echo survived

Exercise 5: under what conditions will this fail?

   1 set -e
   2 read -r foo < configfile

(Answers)

But wait, there’s more!

Even if you use expr(1) (which we do not recommend — use arithmetic expressions instead), you still run into the same problem:

   1 set -e
   2 foo=$(expr 1 - 1)
   3 
   4 echo survived

Subshells from command substitution unset set -e, however (unless inherit_errexit is set with Bash 4.4):

   1 set -e
   2 foo=$(expr 1 - 1; true)
   3 
   4 echo survived

Note that set -e is not unset for commands that are run asynchronously, for example with process substitution:

   1 set -e
   2 mapfile foo < <(true; echo foo)
   3 echo ${foo[-1]} 
   4 mapfile foo < <(false; echo foo)
   5 echo ${foo[-1]} 

Another pitfall associated with set -e occurs when you use commands that look like assignments but aren’t, such as export, declare, typeset or local.

   1 set -e
   2 f() { local var=$(somecommand that fails); }
   3 f    
   4 
   5 g() { local var; var=$(somecommand that fails); }
   6 g    

In function f, the exit status of somecommand is discarded. It won’t trigger the set -e because the exit status of local masks it (the assignment to the variable succeeds, so local returns status 0). In function g, the set -e is triggered because it uses a real assignment which returns the exit status of somecommand.

A particularly dangerous pitfall with set -e is combining functions with conditionals. The following snippets will not behave the same way:

   1 set -e
   2 f() { false; echo "This won't run, right?"; }
   3 f
   4 echo survived
   1 set -e
   2 f() { false; echo "This won't run, right?"; }
   3 if f; then  
   4     echo survived
   5 fi

As soon as a function is used as a conditional (in a list or with a conditional test or loop) set -e stops being applied within the function. This may not only cause code to unexpectedly start executing in the function but also change its return status!

Using Process substitution, the exit code is also discarded as it is not visible from the main script:

   1 set -e
   2 cat <(somecommand that fails)
   3 echo survived

Using a pipe makes no difference, as only the rightmost process is considered:

   1 set -e
   2 somecommand that fails | cat -
   3 echo survived

set -o pipefail is a workaround by returning the exit code of the first failed process:

   1 set -e -o pipefail
   2 failcmd1 | failcmd2 | cat -
   3 
   4 echo survived

though with pipefail in effect, code like this will sometimes cause an error, depending on whether the output of somecmd exceeds the size of the pipe buffer or not:

   1 set -e -o pipefail
   2 somecmd | head -n1
   3 
   4 echo survived

So-called strict mode

In the mid 2010s, some people decided that the combination of set -e, set -u and set -o pipefail should be used by default in all new shell scripts. They call this unofficial bash strict mode, and they claim that it “makes many classes of subtle bugs impossible” and that if you follow this policy, you will “spend much less time debugging, and also avoid having unexpected complications in production”.

As we’ve already seen in the exercises above, these claims are dubious at best. The behavior of set -e is quite unpredictable. If you choose to use it, you will have to be hyper-aware of all the false positives that can cause it to trigger, and work around them by “marking” every line that’s allowed to fail with something like ||true.

Conclusions

GreyCat‘s personal recommendation is simple: don’t use set -e. Add your own error checking instead.

rking’s personal recommendation is to go ahead and use set -e, but beware of possible gotchas. It has useful semantics, so to exclude it from the toolbox is to give into FUD.

geirha’s personal recommendation is to handle errors properly and not rely on the unreliable set -e.

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