Category: Over The Top Services

Akash Saksena, one of the Hotstar engineers, posted on a blog what went into making Hostar the smooth streamer it turned out to be during the World Cup. Read on to find out more.

“Your cloud provider also has physical limits of how much you can auto-scale. Work with them closely and ensure you make the right projections ahead of time. Even then, nothing can make it better for you if you are inefficient per server. This calls for rabid tuning of all your system parameters. Moving from development to production environments requires knowledge of what hardware your code will run on and then tweaking it to suit that system. Be lean on your single server and yield results with more room to scale horizontally. Review all your configurations with a fine tooth, it’ll save you the blushes in production. Each system must be tuned specifically to the traffic pattern and hardware you choose to run it on.

No Dumb Clients
At Indian cricket scale, we cannot afford to have clients that rely completely on the server systems to make decisions. Tsunami’s can overwhelm the back-end. Retries will make the problems worse. Clients must be smart about inferring when things don’t look right, and add “jitter” to the requests they make to the servers. Caching, exponential back-offs and panic protocols all come together to ensure a seamless customer experience.

Three pillars

Our platform has three core pillars, the subscription engine, meta-data engine and our streaming infrastructure. Each of these have unique scale needs and were tweaked separately. We built pessimistic traffic models for each of these basis which we came up with ladders that controlled server farms depending on the estimated concurrency. Knowing what your key pillars are and what kind of patterns they are going to experience is pivotal when it comes to tuning. One size does not fit all.

Once Only

Scaling effectively at such a scale means that you drive away as much traffic as possible from the origin servers. Depending on your business patterns, using caching strategies on the serving layer as well as smart TTL controls on the client end, one can give breathing room to their server systems.

Reject Early

Security is a key tenet, and we leverage this layer to also drive away traffic that doesn’t need to come to us at the top of the funnel. Using a combination of white listing and industry best practices, we drive away a lot of spurious traffic up front itself.

The Telescope

Like any other subscription platform, we’re ultimately beholden to the processing rates that our payment partners provide us. Sometimes during a peak, this might mean adding a jitter to our funnel to allow customers to follow through at an acceptable rate to enable a higher success rate overall. Again, these funnels / telescopes are designed keeping in mind the traffic patterns that your platform will experience. Often these decisions will need to involve customer experience changes to account for being gentler on the infrastructure.

The Latency Problem

As the leading OTT player in India, we’ve been steadily making improvements to our streaming infrastructure. It remains a simple motto of leaner on the wire, faster than broadcast. As simple as this sounds, its one of the most complex things to get right. Through the year we have brought down our latency numbers from being roughly 55s behind broadcast, to approximately 15–20s behind broadcast and only a couple of seconds behind on our re-done web platform.

This was a result of highly meticulous measurement of how much time each segment of our encoding workflow took and then tweaking operations and encoder settings to do better. We did this by applying profiling of the workflow to instrument each segment. This is another classical tenet, tuning cannot happen without instrumentation.

We continue to tweak bit-rate settings to provide a un-compromised experience to our customers while at the same time be efficient in bandwidth consumption for Indian conditions.

Lower latencies and smarter use of player controls to provide a smooth viewing experience to customers also helps with smoother traffic patterns as fewer customers are repeating the funnel, which can cause a lot of ripple through the whole system with it’s retries and consequent additional events that pass through the system.

Server Morghulis (aka Client Resiliency)

The Hotstar client applications have been downloaded multiple hundred million times so far. Suffice to say that when game time comes, millions of folks are using Hotstar as their primary screen. Dealing with such high concurrency means that we cannot think of a classical coupling of client with the back-end infrastructure.

We build our client applications to be resilient and gracefully degrade. While we maintain a very high degree of availability, we also prepare for the worst by reviewing all the client : server interactions and indicating either gracefully that the servers were experiencing high load or by a variety of panic switches in the infrastructure. These switches indicate to our client applications that they should ease off momentarily, either exponential back-off or sometimes a custom back-off depending on the interaction so as to build a jitter into the system that provides the back-end infrastructure time to heal.

While the application has many capabilities, our primary function is that to render video to our customers reliably. If things don’t look completely in control, specific functionality can degrade gracefully and keep the primary function un-affected.

Ensure that the primary function always works and ensure resiliency around server touch-points. Not every failure is fatal, and using intelligent caching with the right TTL’s can buy a lot of precious headroom. This is an important tenet.