At a glance
- Did you know
- Protected video is encrypted once; the player fetches a short-lived key from a license server before it can play.
- Rule of thumb
- Cache license responses per device for a few minutes so a restart does not hit the server again.
- Watch out
- Every playback start waits on it; a key-server outage stops all new plays.
Its settings in ScaleMySystems
What you can change on it in the lab, and what each number does.
- Concurrency (slots)
- Calls it can work on at once (per instance when autoscaling). Needed slots ≈ calls per second × seconds each takes. Extra calls wait in the queue, then are rejected.
- Queue capacity
- Calls allowed to wait for a free slot. A bigger queue absorbs bursts but adds waiting time; 0 rejects straight away.
- vCPU
- CPU cores available. Needed ≈ calls per second × CPU per request ÷ 1000. Above about 90% busy it slows down and may crash.
- CPU per request (ms)
- CPU time each call burns. Part of what the component is; make the code cheaper to lower it.
- Latency (p50) (ms)
- Typical time one call takes here, before any calls it makes itself. Slots are held for this long.
- Latency (p99) (ms)
- The slowest 1% of calls. Callers must set their timeout above this or they cut off healthy calls.
- Timeout to dependencies (ms)
- How long it waits for each call it makes before giving up. Set it above the dependency’s p99 but low enough that a dead dependency does not hold every slot.
- Error rate
- Share of calls that fail on their own (bugs, declines, flaky tools). An agent that calls it on every step multiplies this.
- Quota (req/min)
- Calls allowed per minute (an API key or provider limit). Calls over it get 429s. Needed = calls per second × 60, with headroom.
Problems that start with it
- Premiere night: video at three times the traffic Asked at Netflix and YouTube. Every video segment is served by origin servers reading object storage, manifests come from Postgres, and DRM licenses from license servers, all through the same origin fleet. At 6 s a premiere starts and traffic triples for 12 seconds; at 13 s the segment storage is unavailable for 4 seconds.
- Netflix: from launch build to real traffic Netflix without Open Connect or EVCache: every request reaches the origin, title metadata is read from the catalog database each time, and the playback, browse, license and recommendation services are an eighth of their real size. 6,000 requests a second: half are playback starts, 45% browsing, 5% DRM licenses. Playback starts fail.
Full lesson coming soon
Lessons are being added one component at a time: how it works, its settings, a live exercise to break and fix it, interview questions and a short check. See the Circuit breaker lesson for what one looks like.