@@ -52,7 +52,7 @@ The process-bound coverage project contains exactly five suite files. Thirty-two
Complete serial Linux, macOS, and Windows references run only when `master` moves. Pull requests use the enterprise required path plus standard-hosted compatibility jobs, while other larger-runner sizes run only by manual dispatch.
An additional serial Linux reference runs on the in-house self-hosted pool (`vm-backup` label: a 64-core VM with six always-on systemd-managed runner instances) on every `master` push. It is a hot-standby drill, not a required check: each run re-proves that the persistent VM can execute the complete unsharded aggregate. The actual switch is pre-wired: the three required Linux jobs resolve their pool through the writer-manageable `DSH_CI_FAILOVER` repository variable, so an outage response is setting one variable and re-running — no merge, which would be deadlocked behind the failing checks themselves ([runbook](2026-07-26-ci-failover-runbook.md)). The standby lane is push-triggered, so it always executes the base branch's workflow definition. Under failover, however, `pull_request` jobs do reach these runners with the PR merge ref's own workflow definition — the trust boundary is repository membership (the repository is private with forking disabled, and the selectors exclude Dependabot), as the [failover runbook](2026-07-26-ci-failover-runbook.md) records.
An additional serial Linux reference runs on the in-house self-hosted pool (`vm-backup` label: a 64-core VM with six always-on systemd-managed runner instances) on every `master` push. It is a hot-standby drill, not a required check: each run re-proves that the persistent VM can execute the complete unsharded aggregate. The actual switch is pre-wired: the three required Linux jobs resolve their pool through the writer-manageable `DSH_CI_FAILOVER_LINUX` repository variable, so an outage response is setting one variable and re-running — no merge, which would be deadlocked behind the failing checks themselves ([runbook](2026-07-26-ci-failover-runbook.md)). The standby lane is push-triggered, so it always executes the base branch's workflow definition. Under failover, however, `pull_request` jobs do reach these runners with the PR merge ref's own workflow definition — the trust boundary is repository membership (the repository is private with forking disabled, and the selectors exclude Dependabot), as the [failover runbook](2026-07-26-ci-failover-runbook.md) records.
@@ -6,11 +6,11 @@ English | [中文](2026-07-26-ci-failover-runbook.zh.md)
## Problem
The three required Linux worker jobs in [CI](../../../../.github/workflows/ci.yml) (`node 24 / static`, `node 24 / coverage`, `node 24 / snapshots and artifacts`) run on the hosted enterprise 32-core pools; the required verdict job that aggregates them (`all checks passed`) runs on standard `ubuntu-latest`; the independent native Windows job (`windows node 24 / native complete`) runs on the hosted `dsh-windows-2025-16core` larger runner. When the enterprise pools degrade — jobs queue indefinitely or the enterprise labels vanish — every open pull request becomes unmergeable, and the ordinary recovery of merging a fix is itself deadlocked behind the very required checks that cannot run. **Scope: this switch recovers an enterprise Linux-pool outage AND a hosted Windows-pool outage.** The verdict's other required dependencies (`node-compat`, `python-sdk`, `windows`) stay on standard hosted runners by design (the portable boundary); in a broader GitHub-hosted capacity failure that also takes out the standard pools, those dependencies still block `all checks passed`. An outage therefore needs a switch any responder with repository write access can throw without merging anything.
The three required Linux worker jobs in [CI](../../../../.github/workflows/ci.yml) (`node 24 / static`, `node 24 / coverage`, `node 24 / snapshots and artifacts`) run on the hosted enterprise 32-core pools; the required verdict job that aggregates them (`all checks passed`) runs on standard `ubuntu-latest`; the independent native Windows job (`windows node 24 / native complete`) runs on the hosted `dsh-windows-2025-16core` larger runner. When the enterprise pools degrade — jobs queue indefinitely or the enterprise labels vanish — every open pull request becomes unmergeable, and the ordinary recovery of merging a fix is itself deadlocked behind the very required checks that cannot run. **Scope: two independent switches, one per platform.**`DSH_CI_FAILOVER_LINUX` recovers an enterprise Linux-pool outage (the three required Linux workers plus the `all checks passed` verdict); `DSH_CI_FAILOVER_WINDOWS` recovers a hosted Windows-pool outage (the native Windows job). A Linux-pool outage need not retarget the native Windows job and vice versa. The verdict's other required dependencies (`node-compat`, `python-sdk`, `windows`) stay on standard hosted runners by design (the portable boundary); in a broader GitHub-hosted capacity failure that also takes out the standard pools, those dependencies still block `all checks passed`. An outage therefore needs a switch any responder with repository write access can throw without merging anything.
## Decision
Each of the three required Linux worker jobs, the independent native Windows job, and the `all checks passed` verdict job — which would otherwise stay queued on the failed pool even after every worker passed — resolves its runner pool through the `DSH_CI_FAILOVER` repository variable. Unset (normal), they run on the hosted enterprise pools. Set to `selfhosted` by any repository writer, all five retarget onto the in-house self-hosted pools: the Linux jobs and verdict onto the `vm-backup` pool, coverage and snapshot concurrency drop to shared-VM bounds, and the hosted-path pnpm cache restores are skipped; the native Windows job onto the `dsh-win-ci` pool. The switch is writer-manageable repository state, not a merge, so it works while every check is red. The in-house pools' readiness is continuously re-proven by the `serial / linux (self-hosted standby)` and `serial / windows (self-hosted standby)` lanes, which run the complete unsharded aggregates on every master push.
Each of the three required Linux worker jobs, the independent native Windows job, and the `all checks passed` verdict job — which would otherwise stay queued on the failed pool even after every worker passed — resolves its runner pool through a repository variable, and the switch is split by platform so an outage on one platform does not retarget the other. The three Linux workers and the `all checks passed` verdict (whose `needs` are the required Linux workers and which runs on the `vm-backup` pool) resolve through `DSH_CI_FAILOVER_LINUX`; the native Windows job resolves through `DSH_CI_FAILOVER_WINDOWS`. Unset (normal), they run on the hosted enterprise pools. Set to `selfhosted` by any repository writer, the corresponding jobs retarget onto the in-house self-hosted pool: under `DSH_CI_FAILOVER_LINUX`, the Linux jobs and verdict move onto the `vm-backup` pool, coverage and snapshot concurrency drop to shared-VM bounds, and the hosted-path pnpm cache restores are skipped; under `DSH_CI_FAILOVER_WINDOWS`, the native Windows job moves onto the `dsh-win-ci` pool. Each switch is writer-manageable repository state, not a merge, so it works while every check is red. The in-house pools' readiness is continuously re-proven by the `serial / linux (self-hosted standby)` and `serial / windows (self-hosted standby)` lanes, which run the complete unsharded aggregates on every master push.
`ci.yml` exempts exactly one event from `cancel-in-progress` (`${{ github.event_name != 'push' }}`), so one master push does not cancel the drill still running from the previous one. Each drill runs its complete unsharded aggregate with one gate worker, which takes longer than the interval between master merges; under unconditional cancellation a drill is superseded before reaching a verdict and the lane yields no readiness evidence for a responder to check.
@@ -28,13 +28,15 @@ The decision belongs at workflow level because cancellation applies to the whole
### Switch (any repository writer, ~1 minute, no merge)
1. Repository **Settings → Secrets and variables → Actions → Variables → New repository variable**: name `DSH_CI_FAILOVER`, value `selfhosted`.
The two switches are independent: flip only the one whose platform is degraded.
1. Repository **Settings → Secrets and variables → Actions → Variables → New repository variable**: name `DSH_CI_FAILOVER_LINUX` (Linux pool outage) or `DSH_CI_FAILOVER_WINDOWS` (Windows pool outage), value `selfhosted`.
2. Retrigger the required jobs so they re-resolve their pool. Jobs already **queued** for the hosted labels do not retarget and cannot be re-run in place, so for the documented indefinite-queue outage, cancel the stuck run and re-run all jobs, or push a new commit; "Re-run failed jobs" only helps once a job has actually failed rather than queued.
3. That is the entire switch. Under failover the workflow also, automatically: drops `DSH_COVERAGE_MAX_WORKERS` to 8 and `DSH_SNAPSHOT_MAX_CONCURRENCY` to 12 (sized for six always-on instances: worst case 6 × 8 = 48 coverage workers on the 64-core VM) (shared-VM contention bounds), and skips the hosted-path pnpm cache restores (the VM's persistent store serves warm installs).
3. That is the entire switch. Under Linux failover the workflow also, automatically: drops `DSH_COVERAGE_MAX_WORKERS` to 8 and `DSH_SNAPSHOT_MAX_CONCURRENCY` to 12 (sized for six always-on instances: worst case 6 × 8 = 48 coverage workers on the 64-core VM) (shared-VM contention bounds), and skips the hosted-path pnpm cache restores (the VM's persistent store serves warm installs). The Windows switch has no such concurrency or cache branches; it only retargets the native Windows job's pool.
#**Dependabot exception.** All five selectors deliberately exclude `dependabot[bot]`: under failover, Dependabot PRs stay queued for the hosted pool rather than executing dependency-supplied code on the persistent VMs. A Dependabot PR that remains queued during an outage is expected behavior, not a failed switch; it completes when the hosted pool recovers.
#**Dependabot exception.** Both switches' selectors deliberately exclude `dependabot[bot]`: under failover, Dependabot PRs stay queued for the hosted pool rather than executing dependency-supplied code on the persistent VMs. A Dependabot PR that remains queued during an outage is expected behavior, not a failed switch; it completes when the hosted pool recovers.
**Who can flip the variable.** GitHub's API lets any collaborator with write access manage repository variables, so the switch is writer-level, not strictly admin-only. In this repository's trust model that is not an escalation: the runner groups admit all workflows of this private, fork-disabled repository (a deliberate trade to make PR-ref failover possible at all), so any writer could already reach the VMs by pushing a branch workflow. The boundary against untrusted code is repository membership; the variable only routes work for members.
**Who can flip the variable.** GitHub's API lets any collaborator with write access manage repository variables, so each switch is writer-level, not strictly admin-only. In this repository's trust model that is not an escalation: the runner groups admit all workflows of this private, fork-disabled repository (a deliberate trade to make PR-ref failover possible at all), so any writer could already reach the VMs by pushing a branch workflow. The boundary against untrusted code is repository membership; the variables only route work for members.
## Capacity during failover
@@ -43,18 +45,18 @@ Six always-on instances absorb normal PR traffic (the pool's steady-state load i
### Switch back
Delete the `DSH_CI_FAILOVER` variable (or set it to anything other than `selfhosted`). New runs resolve back to the hosted enterprise pools. Remove any extra instances that were registered during the incident.
Delete the `DSH_CI_FAILOVER_LINUX` or `DSH_CI_FAILOVER_WINDOWS` variable (or set it to anything other than `selfhosted`). New runs resolve back to the hosted enterprise pools. Remove any extra instances that were registered during the incident.
### Trust boundary
The variable is writer-manageable repository state; a pull request event itself can neither set it nor read a different value into effect, and the selector expressions live in workflow definitions. Note that under failover, `pull_request` runs execute the PR merge ref's own workflow definition — the boundary against untrusted code is repository membership (private, forking disabled, Dependabot excluded by the selectors), not the variable. Note on runner-group policy: pinning the runner group to the master-ref workflow is **incompatible** with this failover — the four failover jobs are `pull_request` runs evaluated from PR merge refs, and a master-pinned group leaves them queued (observed live on 2026-07-27; the group was widened to all workflows of this repository to unblock the switch). A stricter runner-side policy therefore costs PR failover; the shipped posture accepts repository-scoped, all-workflow group access.
The variables are writer-manageable repository state; a pull request event itself can neither set them nor read a different value into effect, and the selector expressions live in workflow definitions. Note that under failover, `pull_request` runs execute the PR merge ref's own workflow definition — the boundary against untrusted code is repository membership (private, forking disabled, Dependabot excluded by the selectors), not the variable. Note on runner-group policy: pinning the runner group to the master-ref workflow is **incompatible** with this failover — the five failover jobs are `pull_request` runs evaluated from PR merge refs, and a master-pinned group leaves them queued (observed live on 2026-07-27; the group was widened to all workflows of this repository to unblock the switch). A stricter runner-side policy therefore costs PR failover; the shipped posture accepts repository-scoped, all-workflow group access.
## Alternatives considered
**Merge a workflow change to switch pools.** Rejected because the outage that motivates the switch is exactly the state in which no PR can merge: the required checks are the ones failing. A repository variable is writer-manageable state that takes effect on re-run without a merge.
**Keep the self-hosted pool always in the required path.** Rejected because it trades hosted-pool availability for the in-house VM's, moving a single point of failure rather than adding a fallback. The variable keeps the hosted pools primary and the self-hosted pool a proven, one-action standby.
**Keep the self-hosted pool always in the required path.** Rejected because it trades hosted-pool availability for the in-house VM's, moving a single point of failure rather than adding a fallback. The variables keep the hosted pools primary and the self-hosted pools proven, one-action standbys; splitting them by platform means an outage on one platform does not retarget the other.
## Consequences
Recovering from a hosted-pool outage is a single variable (any writer) plus a re-run, with no merge on the critical path. The cost is a second runner topology to keep working: the standby lane exercises it on every master push so the failover target never goes stale, and the concurrency and cache-restore branches in `ci.yml` carry a `selfhosted` leg that must stay in step with the hosted leg.
Recovering from a hosted-pool outage is flipping the affected platform's variable (any writer) plus a re-run, with no merge on the critical path. The cost is a second runner topology per platform to keep working: the standby lanes exercise them on every master push so the failover targets never go stale, and the concurrency and cache-restore branches in `ci.yml` carry a `selfhosted` leg (Linux only) that must stay in step with the hosted leg. Splitting the switch by platform adds one more variable to manage but bounds the blast radius of each switch to the jobs of a single platform.
**谁能扳动这个变量。**GitHub 的 API 允许任何具有写权限的协作者管理仓库变量，因此该开关实际是写者级而非严格的管理员级。在本仓库的信任模型下这并不构成升权：runner group 接纳本私有、禁 fork 仓库的全部工作流（这是让 PR 引用的故障切换得以成立的刻意取舍），因此任何写者本就可以通过推送分支工作流触达这台虚拟机。抵御不可信代码的边界是仓库成员资格；变量只是为成员路由工作。
**谁能扳动这个变量。**GitHub 的 API 允许任何具有写权限的协作者管理仓库变量，因此每个开关实际是写者级而非严格的管理员级。在本仓库的信任模型下这并不构成升权：runner group 接纳本私有、禁 fork 仓库的全部工作流（这是让 PR 引用的故障切换得以成立的刻意取舍），因此任何写者本就可以通过推送分支工作流触达这台虚拟机。抵御不可信代码的边界是仓库成员资格；变量只是为成员路由工作。
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