DRM license-server cold-start
during a primetime spike.
A working postmortem on the weekday evening event where the encryption key server had not warmed its certificate cache, license requests stalled for ~9% of the primetime cohort for ~6 minutes, and the Streamwake agentic ops layer caught it from viewer-impact telemetry, ranked it as a license-server cold-start with 91% confidence, and remediated it with a pre-warm plus an entitlement-cache TTL bump — split explicitly into the acts the agent did autonomously and the acts it surfaced to humans.
Book a technical demo for DRM license-server cold-start
Read the postmortem — then bring your own incident to Streamwake.
Two ways to engage on this exact failure pattern: book a 30-minute technical demo where we walk through the probe cascade on your source, or hand us an archived incident and watch the agent diagnose it end-to-end.
Both routes land on the scoping intake form — no SDR gate.
What the cohort saw
The first things to read on any real primetime incident are the cohort-level numbers — how many sessions a player-visible symptom hit, how long, and where the symptom landed on the keyserver path. Three numbers did the heavy lifting here.
Roughly 9% of the eu-west primetime cohort — DRM license requests stalled (rx-timeouts against retry-after: 30): the player’s EME layer dropped to a fallback path; certificate freshness probe latency on the keyserver path spiked.
~6 minutes between the first stalled license at T+0m and the cohort-license-OK-ratio returning within baseline at T+18m. The postmortem window goes longer because the entitlement-cache TTL bump ships on the next deploy — not in the same incident window.
x-keyserver-status: cert-cache-miss-cold-start on cdn-A/fra02. Same cohort hitting manifest green on the same CDN ruled out CDN-side failure as the cause.
How Streamwake classified this incident
Three ranked hypotheses, with the top one filing the timeline and the secondary signal carrying the cause. The cdn_pop lane is included to make explicit that the agent ruled it out — the issue was on the keyserver path, not on the edge.
license_server_cold_start — the encryption-key certificate cache had not been pre-warmed ahead of the primetime spike. Three signals line up: drm.license_reachable burst ratio 0.42 (baseline 0.01), drm.cohort_license_ok_ratio 7.4% vs 91% baseline, drm.cert_freshness_warmed cert.warm_state: cold with cert.freshness_probe_age_h: 13.7.
keyserver_overload was the secondary signal ranked at 6% — the burst ratio matched a cache-miss retry pattern rather than pool exhaustion. The dismissal rule was “rank the cause on signal pattern, not burst alone”; cache-miss retries under a cold cert cache produce the same burst ratio as a keyserver overload, but the cert freshness probe is the decisive signal.
- Region: eu-west
- Status: resolved (window closed)
- Opened: 2026-08-06 19:32 UTC
- Spread: contained to eu-west — na-east cohort unaffected
Above the 80% threshold the agent treats as a confident top-hypothesis filing. cdn_pop · 0.03 was cleared explicitly because manifest served green on the same cohort and the same CDN — the issue was on the keyserver path, not on the edge.
Incident timeline
Ten events: detection on the cohort, classification across three ranked hypotheses, four autonomous acts the agent took on its own, three acts it surfaced to humans, the recovery probe, and the resolution. The right-hand “act” tag is what makes this postmortem distinct from a generic write-up — it pins the split between autonomous agentic ops and the work that genuinely needed a person.
Today
- T+0mDetectionby cohort agent · eu-westact · autonomous
License-fetch burst & cohort OK-ratio collapsed simultaneously
drm.cohort_license_ok_ratio drifted from 91.0% baseline to 7.4% over a 90-second window; drm.license_reachable flipped to fail with burst_ratio 0.42 (baseline 0.01).
Aug 6, 07:32:11 PM - T+1mClassificationby Streamwake reliability agentact · autonomous
Ranked: license_server_cold_start (0.91) · secondary keyserver_overload (0.06)
Top hypothesis reads 91% confidence. Two ranked alternatives dismissed: cdn_pop (manifest served green on the same cohort — CDN healthy), keyserver_overload (pool size normal, burst pattern matches cache-miss retries, not pool exhaustion).
Aug 6, 07:33:11 PM - T+2mAutomated actionby Streamwake reliability agentact · autonomous
Emitted prewarm_keyserver_cert_cache + pin_license_to_alternate_pop_for_failing_region
Pre-warm the encryption-key certificate cache on the keyserver path; pin the next license fetch from cdn-A/fra02 to cdn-B/ams04 (which already had a warm peering topology to the issuer).
Aug 6, 07:34:11 PM - T+2mAutomated actionby Streamwake reliability agentact · autonomous
Horizontal scale-out kick-in on the keyserver pool
Pool size doubled for the affected geo (eu-west); license-fetch concurrency headroom raised from 1.4×b to 3.2×nominal baseline.
Aug 6, 07:34:11 PM - T+4mAutomated actionby Streamwake reliability agentact · autonomous
Rebalance hint queued: extend_entitlement_cache_ttl
Entitlement-cache TTL bumped from 60s to 300s so the second license fetch on the same cohort is served from the entitlement cache, not the keyserver path. Staged for the next day’s deployment.
Aug 6, 07:36:11 PM - T+9mSurfaced to humanby agent → operatoract · surfaced to humans
Operator engaged the DRM vendor on the cert-cache invalidation policy
Vendor confirmed the cert-cache is cold by default and requires an explicit pre-warm after every cert issuance. New policy: cert warm on issuance, not on first-use. Vendor pushed a fix to the cert prefetch daemon.
Aug 6, 07:41:11 PM - T+11mSurfaced to humanby on-callact · surfaced to humans
On-call paged for the cold-cache root-cause review
Page acknowledged within 90s; reviewer confirmed the agent’s rank and the rebalance hints had prevented the cohort from doubling before the pre-warm landed.
Aug 6, 07:43:11 PM - T+14mSurfaced to humanby reliability teamact · surfaced to humans
Postmortem write-up assigned (this page)
Reliability team assigned the public postmortem; this page is the resulting write-up, with the ranked hypotheses, recommended fix, and agentic-act split pinned from the timeline.
Aug 6, 07:46:11 PM - T+18mAutomated actionby Streamwake reliability agentact · autonomous
Re-probed the cohort; cohort_license_ok_ratio returned within baseline
drm.cohort_license_ok_ratio climbed from 7.4% back to 91.4% over the next 90 seconds; drm.cert_freshness_warmed flipped to pass with cert.warm_state: warm.
Aug 6, 07:50:11 PM - T+32mResolutionby Operator + agentact · autonomous
Incident resolved; entitlement-cache TTL bump ships next day
Player-side license failure cleared for the affected cohort; no further 5xx burst on the keyserver path; the entitlement-cache TTL bump and the vendor cert-issuance policy both ship in the next deploy window.
Aug 6, 08:04:11 PM
- classify · ranked three hypotheses with confidence in 90s
- prewarm · emitted prewarm_keyserver_cert_cache on the keyserver path
- pin · emitted pin_license_to_alternate_pop_for_failing_region (cdn-A → cdn-B)
- scale-out · horizontal scale-out kick-in on the keyserver pool (eu-west)
- rebalance · queued extend_entitlement_cache_ttl (60s → 300s) for the next deploy
- operator · engaged the DRM vendor on the cert-cache invalidation policy
- on-call · paged for the cold-cache root-cause review
- reliability team · assigned the public postmortem write-up (this page)
Anatomy of the evidence packet
The two packets on the failing source — a multipart license-fetch envelope on the cold keyserver cache, and the agent timeline response with the ranked hypotheses and the rebalance hints. The envelope is what the agent decided on; the timeline response is what the agent emitted.
POST /widevine/license HTTP/1.1
host: keys.example-cdn.net
content-type: application/octet-stream
x-schema-version: 1.4
x-request-id: cklivedrmcoldstart7734
----- cycle 0 (T+0m, before prewarm) -----
HTTP/2 503
content-type: application/octet-stream
server-timing: license-fetch;dur=412, key-derive;dur=88, cert-verify;dur=2118
x-cdn: cdn-A/fra02
x-keyserver-status: cert-cache-miss-cold-start
retry-after: 30
# cert.freshness_probe_age_h: 13.7
# cert.warm_state: cold
# cohort hit ratio over the 90s window: 7.4% (drift baseline: 91.0%)
----- cycle 0 follow-up (T+0m +1s) -----
HTTP/2 503
content-type: application/octet-stream
server-timing: license-fetch;dur=478, key-derive;dur=92, cert-verify;dur=2210
x-cdn: cdn-A/fra02
x-keyserver-status: cert-cache-miss-cold-start
retry-after: 30
----- cycle 1 (T+0m +4s, after prewarm + pin) -----
HTTP/2 200
content-type: application/octet-stream
server-timing: license-fetch;dur=384, key-derive;dur=104
x-cdn: cdn-B/ams04
x-keyserver-status: warm-from-prewarm
# cert.freshness_probe_age_h: 13.7
# cert.warm_state: warm
# rebalance_hints emitted: prewarm_keyserver_cert_cache, pin_license_to_alternate_pop_for_failing_region
# cohort hit ratio over the 90s window: 91.4% (within baseline)- x-keyserver-status →
cert-cache-miss-cold-start - cert-verify →
dur=2118mson the issuer round-trip - drm.cert_freshness_warmed →
cert.warm_state: cold+freshness_probe_age_h: 13.7 - drm.cohort_license_ok_ratio →
7.4% vs 91% baseline (90s window) - cdn.availability → pass. Manifest served green on the same cohort.
{
"stream_id": "cklivedrmcoldstart7734",
"source": "https://cdn.example.com/live/event/manifest.m3u8",
"protocol": "HLS+DRM",
"checked_at": "2026-08-06T19:32:11Z",
"ranked_hypotheses": [
{
"rank": 1,
"hypothesis": "license_server_cold_start",
"confidence": 0.91,
"evidence_signals": [
"drm.license_reachable → fail (burst_ratio 0.42 over 30s window)",
"drm.cert_freshness_warmed → fail (cert.freshness_probe_age_h: 13.7, cert.warm_state: cold)",
"drm.cohort_license_ok_ratio → fail (7.4% vs 91% baseline over 90s window)",
"cdn.availability → pass (manifest served green on the same cohort)"
]
},
{
"rank": 2,
"hypothesis": "keyserver_overload",
"confidence": 0.06,
"evidence_signals": [
"keyserver pool size normal; burst_ratio consistent with cache-miss retries not pool exhaustion"
]
},
{
"rank": 3,
"hypothesis": "cdn_pop",
"confidence": 0.03,
"evidence_signals": [
"manifest served green on cdn-A; edge.geo_drift pass"
]
}
],
"agent_rebalance_hints": [
"prewarm_keyserver_cert_cache",
"pin_license_to_alternate_pop_for_failing_region",
"rebalance_hints=[extend_entitlement_cache_ttl]",
"horizontal_scale_out_kick_in"
],
"surfaced_to_humans": [
{"owner": "DRM vendor", "task": "engage on cert-cache invalidation policy"},
{"owner": "on-call", "task": "page for the cold-cache root-cause review"},
{"owner": "reliability team", "task": "assign the postmortem write-up"}
]
}- rebalance hint →
prewarm_keyserver_cert_cache - rebalance hint →
pin_license_to_alternate_pop_for_failing_region - rebalance hint →
rebalance_hints=[extend_entitlement_cache_ttl] - scale-out →
horizontal_scale_out_kick_in (eu-west) - surfaced → engaged the DRM vendor on the cert-cache invalidation policy
- surfaced → paged on-call for the cold-cache root-cause review
Pre-warm the cert cache · bump the entitlement-cache TTL
Two changes close the gap the timeline exposed. The first is what the agent already emitted on this incident (the pre-warm + pin); the second is what ships on the next deploy (the entitlement-cache TTL bump). Both are tracked as exported rebalance_hints rows.
The cert prefetch daemon should warm the keyserver’s encryption-key certificate cache on cert issuance, not on first use. The cert in this incident was issued 13.7 hours before the spike, so the daemon had a 13-hour window to pre-warm — it did not. Bump the warm window from “on cohort ramp” to “on cert issuance, ahead of the primetime schedule”.
drm.cert_freshness_warmed flips to cert.warm_state: warm on the same cohort at T-30m before primetime for ten consecutive days; cert-verify;dur stays under 600ms on the first license fetch after ramp.
Entitlement cache TTL was 60s, which forces a second license fetch on the keyserver path every minute per session. Raising the TTL to 300s keeps the second-through-fifth license fetches off the keyserver entirely; only the first fetch per session still hits the keyserver. The cohort impact at the 60s setting is every minute per session; at 300s it drops to every five minutes per session.
drm.cohort_license_ok_ratio drift on the affected geo drops under 2% over a 24-hour window; drm.license_reachable burst ratio stays under 0.02 for ten consecutive 30-second windows.
Want Streamwake to catch this on your primetime cohort?
Sign up, register an HLS+DRM probe, and the same drm.license_reachable · drm.cert_freshness_warmed · drm.cohort_license_ok_ratio probes that produced the timeline above run on every refresh — and surface in a Slack channel, a webhook, or the streams dashboard.
- Pick a recent on-call incident — manifest stall, edge miss, player-side stall, or peer congestion.
- We replay it through the same reliability-agent probe cascade used on the postmortem above.
- You walk away with a written what-could-have-been-Automated readout, not a sales deck.
Read the next postmortem
The other live entries cover ISP-vs-CDN disambiguation, live-sports buffering, and startup-delay regressions on a cross-platform player release.