certctl/docs/deployment-atomicity.md

Deployment Atomicity, Post-Deploy Verification, and Rollback

Deploy-hardening I master bundle (v2.X.0). Operator + integrator reference for the atomic-write + post-deploy TLS verify + rollback pipeline that closes the procurement-checklist gap with commercial competitors (Venafi, DigiCert Certificate Manager, Sectigo).

1. Overview

Before deploy-hardening I, certctl's target connectors used duplicated os.WriteFile flows. A failure mid-deploy could leave a target with a renewed cert but no chain (or vice versa); a reload-fail produced a half-deployed state that required manual rollback; a wrong-vhost cert was silent until users reported it.

Deploy-hardening I closes three procurement-checklist gaps in a single shared primitive:

Gap	Pre-bundle	Post-bundle
Atomic deploy with rollback	F5 only (transactional API)	All 13 connectors via deploy.Apply
Post-deploy TLS verification	None	NGINX/Apache/HAProxy/Traefik/Caddy/Envoy/Postfix all do TLS handshake + SHA-256 fingerprint compare; fail → rollback
Vendor-specific deployment recipes	Light docs	(Bundle II — cowork/deploy-hardening-ii-prompt.md)

This document describes the operator-visible surface. The Go-level contract lives at internal/deploy/doc.go.

2. The atomic-write primitive — Plan / Apply

internal/deploy.Apply(ctx, plan) is the load-bearing entry point. Connectors build a Plan describing one or more files + their PreCommit (validate) and PostCommit (reload) hooks; Apply executes them all-or-nothing.

plan := deploy.Plan{
    Files: []deploy.File{
        {Path: "/etc/nginx/certs/cert.pem", Bytes: certPEM, Mode: 0644},
        {Path: "/etc/nginx/certs/chain.pem", Bytes: chainPEM, Mode: 0644},
        {Path: "/etc/nginx/certs/key.pem",   Bytes: keyPEM,   Mode: 0640},
    },
    PreCommit: func(ctx context.Context, tempPaths map[string]string) error {
        // Run `nginx -t` against the staged config — bytes already
        // written to <path>.certctl-tmp.<unix-nanos>.
        return runValidate(ctx, "nginx -t")
    },
    PostCommit: func(ctx context.Context) error {
        return runReload(ctx, "nginx -s reload")
    },
}
res, err := deploy.Apply(ctx, plan)

Apply's algorithm:

1. Per-file mutex acquired (sync.Map; coarse-grained per-path serialization).
2. SHA-256 idempotency short-circuit. If every File's destination already matches, return Result.SkippedAsIdempotent=true without firing PreCommit/PostCommit.
3. Pre-deploy backup: copy each existing destination to <path>.certctl-bak.<unix-nanos>.
4. Write each File's bytes to <path>.certctl-tmp.<unix-nanos> in the destination directory (same-filesystem rename).
5. Apply ownership (chown + chmod) to each temp file BEFORE rename so the swap is atomic with the right perms.
6. Call PreCommit(ctx, tempPaths). On error: clean up temps; return ErrValidateFailed.
7. os.Rename each temp → final. POSIX guarantees atomic.
8. Call PostCommit(ctx). On error: restore each backup; re-call PostCommit. If second PostCommit also fails: return ErrRollbackFailed (operator-actionable).
9. Janitor: prune backups beyond Plan.BackupRetention (default 3, -1 to disable).

3. Per-connector atomic contract

Connector	PreCommit (validate)	PostCommit (reload)	Post-deploy verify	Quirks
nginx	nginx -t	nginx -s reload	TLS handshake to host:443	Default key mode 0640 (worker reads via group)
apache	apachectl configtest	apachectl graceful	TLS handshake	Default key mode 0600; per-distro user (apache2/apache/httpd)
haproxy	haproxy -c -f <cfg>	systemctl reload haproxy	TLS handshake	Combined PEM (cert+chain+key in one file); default mode 0600
traefik	(none — file watcher)	(none — file watcher auto-reloads)	TLS handshake	atomic-write only; ValidateOnly returns sentinel
caddy (file mode)	(none)	(none — file watcher)	TLS handshake	atomic-write replaces os.WriteFile
caddy (api mode)	Probe admin /config/	POST /load (already atomic at admin server)	(admin server confirms)	ValidateOnly real impl probes admin API
envoy	(none — SDS file watcher)	(none — SDS file watcher)	TLS handshake	atomic-write replaces os.WriteFile
postfix	postfix check	postfix reload	TLS handshake to port 25	Chain appended to cert if no ChainPath
dovecot	doveconf -n	doveadm reload	TLS handshake to port 993	Same code path as postfix
f5	(Authenticate probe)	(Transactional commit)	TLS handshake to VS	Already transactional; rollback automatic via failed commit
iis	(Get-WebSite probe)	(PowerShell cert install)	TLS handshake	Already explicit pre-deploy backup + post-rollback re-import
ssh	(Connect probe)	(SCP upload + remote chmod)	tls.Dial to remote TLS port	Pre-deploy SCP backup of remote files
wincertstore	(Get-ChildItem Cert:)	(Import-PfxCertificate)	(admin probe)	Get-ChildItem snapshot for rollback
javakeystore	(keytool -list)	(keytool -importkeystore)	(admin probe)	keytool snapshot; rollback via keytool -delete + re-import
k8ssecret	(GetSecret RBAC probe)	(Update Secret)	SHA-256 verify of returned Secret	Atomic at API server; kubelet sync polled via Pod.Status.ContainerStatuses

4. Post-deploy TLS verification

Frozen decision 0.3 (deploy-hardening I): post-deploy verify is ON by default when the operator configures PostDeployVerify.Endpoint. Per-target opt-out via PostDeployVerify.Enabled = false.

The connector-side flow:

// After Apply returns successfully, the connector dials the
// configured endpoint, pulls the leaf cert SHA-256, and compares.
res := tlsprobe.ProbeTLS(ctx, "nginx-test:443", 10*time.Second)
if res.Fingerprint != certPEMToFingerprint(deployedCertPEM) {
    // Mismatch — wrong vhost, NGINX serving cached cert,
    // load-balanced target hit a different pod, etc.
    rollbackToBackups(ctx, applyResult.BackupPaths)
    emitAlert("post-deploy verify SHA-256 mismatch")
}

Retry with backoff (default 3 attempts, 2s exponential) defends against load-balanced targets where the verify might hit a different pod that hasn't picked up the new cert yet:

post_deploy_verify:
  enabled: true
  endpoint: "nginx.svc.cluster.local:443"
  timeout: 10s
post_deploy_verify_attempts: 3
post_deploy_verify_backoff: 2s

5. Rollback semantics

Rollback fires automatically on three triggers:

1. PostCommit (reload) fails → Apply restores backups + retries reload. Returns ErrReloadFailed on success (degraded no-op) or ErrRollbackFailed if the second reload also fails.
2. Post-deploy verify fails → Connector manually triggers rollback (Apply already returned successfully). Backups are restored + reload is invoked again. Same escalation path on second failure.
3. Mid-loop rename fails (rare; only with cross-filesystem misuse) → Apply rolls back the renames that already succeeded.

ErrRollbackFailed is operator-actionable. The destination is in a known-bad state; operators must either:

• Restore from Result.BackupPaths manually + run <reload command>
• Push a fresh known-good cert via the next deploy cycle

The certctl_deploy_rollback_total{outcome="also_failed"} metric is the alert target.

6. ValidateOnly — dry-run mode

target.Connector.ValidateOnly(ctx, request) runs the validate step without touching the live cert. Connectors that can't dry-run (Traefik / Envoy / Caddy file mode) return target.ErrValidateOnlyNotSupported.

Connector	ValidateOnly
nginx	nginx -t
apache	apachectl configtest
haproxy	haproxy -c -f <cfg>
postfix/dovecot	postfix check / doveconf -n
caddy (api)	GET /config/ probe
caddy (file) / traefik / envoy	ErrValidateOnlyNotSupported
f5	client.Authenticate() probe
iis	Get-WebSite -Name <SiteName>
ssh	client.Connect() probe
wincertstore	Get-ChildItem Cert:\<loc>\<store>
javakeystore	keytool -list -keystore <path>
k8ssecret	client.GetSecret() RBAC probe

Operators preview a deploy via the agent's --dry-run flag (or the equivalent CLI invocation).

7. File ownership + mode preservation

The single most common silent-failure mode pre-bundle: agent runs as root, calls os.WriteFile(path, bytes, 0600), locks NGINX out of the existing nginx:nginx 0640 key file.

Per frozen decision 0.7, deploy.Apply resolves ownership via this precedence:

1. Explicit File.Mode / File.Owner / File.Group (per-target config) → use as given.
2. Existing destination file → preserve its chown + chmod.
3. Plan.Defaults.Mode / .Owner / .Group → use as fallback for new files.
4. Nothing set → os.WriteFile default (0644) for new files; preserved for existing.

Per-connector defaults (cross-distro, fall back to no-chown if no candidate user exists):

Connector	Default user	Default group	Default cert mode	Default key mode
nginx	nginx → www-data	nginx → www-data	0644	0640
apache	apache → www-data → httpd	same	0644	0600
haproxy	haproxy	haproxy	n/a (combined PEM)	0600
postfix	postfix → dovecot → _postfix	same	0644	0600
traefik	(none)	(none)	0644	0600
envoy	(none)	(none)	0644	0600
caddy	(none)	(none)	0644	0600

8. Per-target deploy mutex

Phase 2 of the master bundle: the agent (cmd/agent/main.go) serializes concurrent deploys to the same target ID via a sync.Map[targetID]*sync.Mutex. Granularity per frozen decision 0.5: one mutex per target, NOT per (target, cert).

Cert deploy throughput is operator-grade tens-per-minute. Coarse serialization is fine and simplifies reasoning about reload-side race windows.

9. Idempotency via SHA-256

Every deploy.Apply short-circuits when all File destinations already match SHA-256 of the new bytes. PreCommit + PostCommit do not fire; backups are not created; the result reports SkippedAsIdempotent = true.

Defends against agent-restart retry storms that would otherwise hammer targets with no-op reloads. Operator-visible signal: certctl_deploy_idempotent_skip_total{target_type="..."}.

10. Troubleshooting matrix

Symptom	Root cause	Operator action
ErrValidateFailed: nginx -t failed	Validate command rejected the staged config	Read PreCommit's wrapped error for the nginx stderr; fix config
ErrReloadFailed: nginx -s reload failed; rolled back	Reload command failed; rollback succeeded; serving the OLD cert	Investigate why reload failed; re-deploy when fixed
ErrRollbackFailed	Reload AND rollback both failed; in known-bad state	Restore from Result.BackupPaths manually; run reload command directly; check disk space + ownership
post-deploy TLS verify SHA-256 mismatch	New cert deployed but a different cert is being served (cached, wrong vhost, stale pod in load balancer)	Check NGINX SSL session cache TTL; verify SNI; bump verify retries via PostDeployVerifyAttempts
chown ... permission denied (in agent log)	Non-root agent OR target user doesn't exist on host	Verify agent runs as root in production; check distro user (Debian: www-data, RHEL: nginx)
Backups accumulating in cert dir	BackupRetention misconfigured	Set BackupRetention: 3 (default) or higher on per-target config
File world-readable after deploy	Default mode 0644 applied to new key file	Set explicit KeyFileMode: 0640 (NGINX) or KeyFileMode: 0600 (Apache)

11. V3-Pro deferrals

Out of scope for the V2-free deploy-hardening I bundle:

• Multi-region deployment coordination — orchestration of N data-center deploys with operator approval gates per stage.
• Cert-pinning verification against mobile-app pin manifests.
• SOC 2 evidence-report generator — auto-export of the deploy audit trail in the format SOC 2 auditors expect.
• Customer-paid validation matrices — vendor-version certified quirks (e.g. "tested on F5 v15.1 + v17.0 + v17.5"). See cowork/deploy-hardening-ii-prompt.md for the per-vendor edge-case audit + integration test sidecars.

12. Per-connector quick reference

Paste-able config snippets for the most-used connectors. Full field reference at docs/connectors.md.

NGINX

target_type: nginx
target_config:
  cert_path: /etc/nginx/certs/cert.pem
  chain_path: /etc/nginx/certs/chain.pem
  key_path: /etc/nginx/certs/key.pem
  reload_command: "nginx -s reload"
  validate_command: "nginx -t"
  cert_file_mode: 0644
  key_file_mode: 0640
  post_deploy_verify:
    enabled: true
    endpoint: "nginx.example.com:443"
    timeout: 10s
  backup_retention: 3

HAProxy

target_type: haproxy
target_config:
  pem_path: /etc/haproxy/certs/cert.pem
  reload_command: "systemctl reload haproxy"
  validate_command: "haproxy -c -f /etc/haproxy/haproxy.cfg"
  pem_file_mode: 0600
  post_deploy_verify:
    enabled: true
    endpoint: "haproxy.example.com:443"

Traefik (file watcher; no reload command)

target_type: traefik
target_config:
  cert_dir: /etc/traefik/certs
  cert_file: cert.pem
  key_file: key.pem
  post_deploy_verify:
    enabled: true
    endpoint: "traefik.example.com:443"

See per-connector tests at internal/connector/target/<name>/<name>_atomic_test.go for the full failure-mode matrix each connector handles.