Synapse on GKE Autopilot

Synapse is the reference Matrix homeserver — the open-source, Apache 2.0-licensed Python server for the Matrix protocol, an open standard for decentralized, federated real-time communication (secure chat and VoIP). This module deploys Synapse on GKE Autopilot on top of the App_GKE foundation, which provisions and manages the shared Google Cloud and Kubernetes infrastructure. Users connect to the homeserver with a Matrix client such as the Element web app.

This guide focuses on the cloud services Synapse uses and how to explore and operate them from the Google Cloud Console and the command line. For the mechanics common to every GKE application — Workload Identity, ingress, autoscaling, CI/CD, Cloud Armor, IAP, Binary Authorization, VPC Service Controls, backups, and the deployment lifecycle — refer to the App_GKE foundation guide rather than repeating them here.

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1. Overview

Synapse runs as a Python web workload. The deployment wires together a focused set of Google Cloud services:

Capability	Google Cloud service	Notes
Compute	GKE Autopilot	Python pods, 2 vCPU / 4 GiB by default, at least 1 replica
Database	Cloud SQL for PostgreSQL 15	Required — Synapse does not support MySQL; database must use C collation
Object storage	Cloud Storage	A dedicated data bucket provisioned automatically
Persistent files	NFS (Filestore)	Signing key + media repository under the data directory; enabled by default
Secrets	Secret Manager	Auto-generated registration shared secret; database password
Ingress	Cloud Load Balancing	External LoadBalancer, optional custom domain + managed certificate

Sensible defaults worth knowing up front:

• PostgreSQL 15 is mandatory, with C collation. The engine is fixed by the shared application layer, and the first-deploy db-init job creates the database with LC_COLLATE='C' LC_CTYPE='C' — Synapse refuses to start against any other collation.
• Synapse self-manages its schema. There is no separate migrate job; Synapse creates and upgrades its own schema automatically on every start.
• homeserver.yaml and the signing key are generated on first boot. The cloud entrypoint generates the config plus a persistent signing key into the data directory and wires the platform PostgreSQL before starting Synapse.
• The signing key must persist. Regenerating it breaks federation and invalidates all device sessions, so the data directory is backed by persistent NFS storage (enable_nfs = true by default). For per-pod durability a StatefulSet PVC can be used.
• server_name is immutable. It is the domain in every user ID (@user:server_name) and in federation. The default (matrix.local) is a placeholder — override it with your real domain before production.
• The container port and all probes must be 8008. Synapse's client + federation listener is set to 8008 in the generated config; the container port and the Kubernetes startup/liveness/readiness probes must all target 8008 or the pod never becomes Ready even though the homeserver is healthy.
• At least 1 replica is maintained. GKE does not scale to zero, which suits a federating homeserver that must stay reachable. A PodDisruptionBudget keeps it available through node upgrades.
• Session affinity is ClientIP by default. Keeps a client's requests on the same pod.
• Redis is not used. Synapse runs a single main process backed entirely by PostgreSQL.
• Admin users are created out-of-band. Open self-service registration is off by default; create users with register_new_matrix_user and the registration shared secret in Secret Manager.

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2. Google Cloud Services & How to Explore Them

All commands assume you have run gcloud container clusters get-credentials <cluster> --region <region> --project <project> and that PROJECT, REGION, and NAMESPACE are set. The namespace and other identifiers are reported in the deployment Outputs.

A. GKE Autopilot — the Synapse workload

Synapse pods are scheduled on Autopilot, which bills for the CPU/memory the pods actually request. Horizontal Pod Autoscaling sizes the deployment between the minimum and maximum replica counts.

• Console: Kubernetes Engine → Workloads → select the Synapse workload to see pods, revisions, and events. Kubernetes Engine → Services & Ingress shows the external IP.
• CLI:

  kubectl get pods,svc,hpa -n "$NAMESPACE"
  kubectl logs -n "$NAMESPACE" deploy/<service-name> --tail=100
  kubectl describe hpa -n "$NAMESPACE"

See App_GKE for how Autopilot, scaling, and the workload type (Deployment vs StatefulSet) are managed.

B. Cloud SQL for PostgreSQL 15

Synapse stores all homeserver state (accounts, rooms, events, device keys, federation state) in a managed Cloud SQL for PostgreSQL 15 instance. Pods reach it privately through the Cloud SQL Auth Proxy sidecar over a 127.0.0.1 loopback; no public IP is exposed. On first deploy a db-init Job creates the application database with C collation and the application user.

• Console: SQL → select the instance for connections, backups, flags, and metrics.
• CLI:

  gcloud sql instances list --project "$PROJECT"
  gcloud sql instances describe <instance-name> --project "$PROJECT"
  gcloud sql connect <instance-name> --user=<db-user> --database=<db-name> --project "$PROJECT"
  # Verify the mandatory collation:
  #   SELECT datname, datcollate, datctype FROM pg_database WHERE datname = '<db-name>';

The instance name, database, user, and the Secret Manager secret holding the password are all surfaced in the Outputs. For the connection model, automated backups, and password rotation, see App_GKE.

C. Cloud Storage & the persistent data directory

A dedicated Cloud Storage data bucket is provisioned automatically. Synapse's own runtime state — homeserver.yaml, the conf.d overrides, the signing key, and the media repository — lives under the data directory (SYNAPSE_DATA_DIR = /data), backed by the NFS (Filestore) volume mounted at the configured mount path.

• Console: Cloud Storage → Buckets; Filestore → Instances.
• CLI:

  gcloud storage buckets list --project "$PROJECT"
  gcloud filestore instances list --project "$PROJECT"
  kubectl get pvc -n "$NAMESPACE"          # if using a StatefulSet PVC

See App_GKE for CMEK options and GCS Fuse mounts.

D. Secret Manager

A registration shared secret is generated automatically and stored in Secret Manager; it backs register_new_matrix_user for out-of-band account creation. The database password is managed separately by the foundation. Secrets are materialised into the namespace via the Secret Store CSI driver.

• Console: Security → Secret Manager.
• CLI:

  gcloud secrets list --project "$PROJECT" --filter="name~synapse"
  kubectl get secrets -n "$NAMESPACE"

See App_GKE for the Secret Store CSI integration and rotation.

E. Networking & ingress

By default the workload is exposed through an external Cloud Load Balancing IP. Matrix client and federation traffic require public reachability. A custom domain with a Google-managed certificate (the domain should match server_name) can be enabled, and a static IP can be reserved so the address survives redeploys.

• Console: Network services → Load balancing; VPC network → IP addresses.
• CLI:

  kubectl get ingress,svc -n "$NAMESPACE"
  gcloud compute addresses list --project "$PROJECT"

See App_GKE for custom domains, Cloud CDN, and static IP details.

F. Cloud Logging & Monitoring

Pod stdout/stderr flow to Cloud Logging; GKE and Cloud SQL metrics flow to Cloud Monitoring. Optional uptime checks and alert policies are available.

• Console: Logging → Logs Explorer; Monitoring → Dashboards / Alerting.
• CLI:

  gcloud logging read 'resource.type="k8s_container" AND resource.labels.namespace_name="'"$NAMESPACE"'"' \
    --project "$PROJECT" --limit 50

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3. Synapse Application Behaviour

• First-deploy database setup. A db-init Job runs db-init.sh using postgres:15-alpine. It connects through the Cloud SQL Auth Proxy and idempotently creates the application role and the database with C collation (LC_COLLATE='C' LC_CTYPE='C' TEMPLATE template0). The job is safe to re-run.
• No migrate job — schema self-managed. Synapse creates and upgrades its schema on every start, so upgrading the application version applies schema changes without a separate migration step.
• Config + signing key generated on first boot. The cloud entrypoint generates homeserver.yaml and a persistent signing key into /data, writes a conf.d snippet wiring PostgreSQL (via the 127.0.0.1 Auth Proxy sidecar) and the 0.0.0.0:8008 listener, then execs Synapse. The signing key is generated only once — keep /data on a persistent volume (NFS by default, or a StatefulSet PVC).
• server_name is immutable after first boot. Set your real domain before the first deploy. Changing it later invalidates every user ID, device session, and federation relationship.
• Container port and probes must be 8008. The Deployment container port and the startup/liveness/readiness probes all target 8008; a mismatch means the probe hits a dead port and the pod never becomes Ready.
• Health path. Probes default to / on 8008 — Synapse serves an unauthenticated landing page there; /health (returns OK) also works as a probe path. Confirm the client API is serving with GET /_matrix/client/versions:

  EXTERNAL_IP=$(kubectl get svc -n "$NAMESPACE" \
    -o jsonpath='{.items[?(@.spec.type=="LoadBalancer")].status.loadBalancer.ingress[0].ip}')
  curl -s "http://${EXTERNAL_IP}/_matrix/client/versions"

• Create the first admin user with the Matrix registration tool from inside a pod:

  kubectl exec -n "$NAMESPACE" deploy/<service-name> -- \
    register_new_matrix_user -c /data/homeserver.yaml -u admin -a http://localhost:8008

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4. Configuration Variables

Variables are grouped exactly as they appear on the deployment platform. Only settings specific to or notable for Synapse are listed; every other input is inherited from App_GKE with its standard behaviour and defaults.

Group 1 — Project & Identity

Variable	Default	Description
project_id	(required)	Target Google Cloud project.
region	us-central1	Region for the workload and regional resources.

Group 2 — Deployment Environment

Variable	Default	Description
tenant_deployment_id	demo	Short suffix that makes resource names unique per environment.
support_users	[]	Emails granted project access and monitoring alerts.
resource_labels	{}	Labels applied to all resources for cost/ownership tracking.

Group 3 — Application Identity

Variable	Default	Description
application_name	synapse	Base name for resources. Do not change after first deploy.
application_display_name	Synapse Helpdesk	Human-readable name.
application_version	latest	Synapse image tag; pin to a specific release (e.g. v1.119.0) in production.

Group 4 — Runtime & Scaling

Variable	Default	Description
deploy_application	true	Set false to provision infrastructure only.
container_port	8008	Synapse's client + federation listener. Probes must match this.
min_instance_count	1	Minimum replicas; keep at 1 so the homeserver is always reachable for federation.
max_instance_count	5	Maximum replicas.
enable_cloudsql_volume	true	Cloud SQL Auth Proxy sidecar for connections.
container_image_source	custom	Thin custom build FROM matrixdotorg/synapse.
enable_image_mirroring	true	Mirror the Synapse base image into Artifact Registry.
enable_vertical_pod_autoscaling	false	VPA for automatic request adjustment.

Group 5 — Environment Variables & Secrets

Variable	Default	Description
environment_variables	{}	Extra non-secret settings. Core SYNAPSE_* values are set automatically.
secret_environment_variables	{}	Map of env var → Secret Manager secret name.
secret_propagation_delay	30	Seconds to wait after secret creation before proceeding.
secret_rotation_period	2592000s	Secret Manager rotation notification frequency.

Group 6 — GKE Backend & Cluster

Variable	Default	Description
service_type	LoadBalancer	External IP for Matrix client + federation traffic.
workload_type	null (auto)	Deployment or StatefulSet; when unset, resolves to Deployment unless stateful_pvc_enabled = true (then StatefulSet).
session_affinity	ClientIP	Sticky routing keeps a client on the same pod.
network_tags	["nfsserver"]	Required when enable_nfs = true.
termination_grace_period_seconds	60	Seconds to wait after SIGTERM before SIGKILL.
enable_network_segmentation	false	Create Kubernetes NetworkPolicy resources.

Group 7 — StatefulSet

Variable	Default	Description
stateful_pvc_enabled	null (off)	Enable PVC templates — useful to give the signing key + media per-pod persistence.
stateful_pvc_size	10Gi	Per-pod PVC storage size.
stateful_pvc_mount_path	/data	Container mount path for the PVC (the Synapse data directory).
stateful_pvc_storage_class	standard-rwo	Kubernetes StorageClass for PVCs.
stateful_headless_service	null (auto)	Create a headless Service for stable pod DNS names.
stateful_pod_management_policy	null (→ OrderedReady)	Pod creation order.
stateful_update_strategy	null (auto)	Update strategy (RollingUpdate or OnDelete).

Group 9 — Reliability Policies

Variable	Default	Description
enable_pod_disruption_budget	true	Protect availability during node upgrades.
pdb_min_available	1	Minimum pods available during voluntary disruptions.

Group 10 — Observability & Health

Variable	Default	Description
startup_probe	HTTP / on 8008, 60s initial delay	Startup probe. Allow first-boot schema setup time.
liveness_probe	HTTP / on 8008, 60s initial delay	Liveness probe.
uptime_check_config	disabled	Optional Cloud Monitoring uptime check.
alert_policies	[]	Optional metric alert policies.

Group 11 — Jobs & Scheduled Tasks

Variable	Default	Description
initialization_jobs	[]	Leave empty to use the built-in db-init job (C-collation database + role).
cron_jobs	[]	Scheduled Kubernetes CronJobs.
additional_services	[]	Sidecar or helper services deployed alongside Synapse.

Group 12 — CI/CD & GitHub Integration

Standard App_GKE Cloud Build / Cloud Deploy integration — see App_GKE. Key inputs: enable_cicd_trigger, github_repository_url, github_token, enable_cloud_deploy.

Group 13 — Filesystem (NFS)

Variable	Default	Description
enable_nfs	true	Persistent NFS for the data directory (signing key + media).
nfs_mount_path	/opt/synapse/storage	Mount path inside the container.

Group 14 — Cloud Storage & Artifact Registry

Variable	Default	Description
create_cloud_storage	true	Create the configured GCS buckets.
storage_buckets	[{ name_suffix = "data" }]	Buckets to provision — the default creates the dedicated data bucket.
gcs_volumes	[]	GCS Fuse volume mounts via the CSI driver.
manage_storage_kms_iam / enable_artifact_registry_cmek	false	CMEK options.
max_images_to_retain / delete_untagged_images / image_retention_days	(set)	Artifact Registry cleanup policy.

Group 15 — Redis

Variable	Default	Description
enable_redis	false	Synapse uses a PostgreSQL-backed queue/cache — leave false unless externalizing.
redis_host / redis_port / redis_auth	"" / 6379 / ""	Redis endpoint (only when externalizing).

Group 16 — Database Backend

Variable	Default	Description
application_database_name	synapse	PostgreSQL database name. Immutable after first deploy.
application_database_user	synapse	Application database user. Immutable after first deploy.
database_password_length	32	Generated password length (16–64).
enable_auto_password_rotation	false	Zero-downtime DB password rotation.
rotation_propagation_delay_sec	90	Seconds to wait after rotation before rolling-restarting pods.

Group 17 — Backup & Maintenance

Variable	Default	Description
backup_schedule	0 2 * * *	Automated backup cron (UTC).
backup_retention_days	7	Retention; raise to 30–90 for production/compliance.
enable_backup_import / backup_source / backup_uri / backup_format	restore options	Restore from a backup on deploy.

Group 18 — Custom SQL Scripts

enable_custom_sql_scripts, custom_sql_scripts_bucket, custom_sql_scripts_path, custom_sql_scripts_use_root — run SQL from a GCS bucket after provisioning. See App_GKE.

Group 19 — Custom Domain, Static IP & Networking

Variable	Default	Description
enable_custom_domain	true	Provision Ingress for custom hostnames + managed certificate (should match server_name).
application_domains	[]	Hostnames to serve.
reserve_static_ip	true	Stable external IP across redeploys.
network_tags	["nfsserver"]	Firewall tags; nfsserver required for NFS.

Group 20 — Identity-Aware Proxy (IAP)

Warning: Enabling IAP requires Google identity authentication for all inbound requests, including Matrix federation and external clients. Only enable IAP for admin-only/private homeservers that do not federate.

Variable	Default	Description
enable_iap	false	Require Google sign-in in front of Synapse.
iap_authorized_users / iap_authorized_groups	[]	Who may access.
iap_oauth_client_id / iap_oauth_client_secret	""	Required when IAP is enabled (sensitive).

Group 21 — Cloud Armor

Variable	Default	Description
enable_cloud_armor	false	Attach a Cloud Armor (WAF) policy to the Ingress backend.
admin_ip_ranges	[]	CIDRs allowed privileged access.
cloud_armor_policy_name	default-waf-policy	Policy name.
enable_cdn	false	Enable Cloud CDN on the GKE Ingress backend (useful for media).

Group 22 — VPC Service Controls & Audit Logging

Variable	Default	Description
enable_vpc_sc	false	Enforce a VPC-SC perimeter (requires organization_id).
vpc_cidr_ranges / vpc_sc_dry_run	(set)	Access level CIDRs / dry-run mode.
enable_audit_logging	false	Detailed Cloud Audit Logs.

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5. Outputs

These values are returned on a successful deployment and are the quickest way to locate and explore the running resources.

Output	Description
service_name	Kubernetes Service name.
namespace	Namespace the workload runs in.
service_cluster_ip	In-cluster ClusterIP.
stage_service_cluster_ips	Map of ClusterIPs for stage-specific services.
service_external_ip	External LoadBalancer IP (when a static IP is reserved).
service_url	URL to reach Synapse.
database_instance_name	Cloud SQL instance name.
database_name	Application database name.
database_user	Application database user.
database_password_secret	Secret Manager secret holding the DB password.
database_host / database_port	DB endpoint (127.0.0.1 via the Auth Proxy) / port.
storage_buckets	Created Cloud Storage buckets.
network_name / network_exists / regions	VPC network, presence, available regions.
container_image / container_registry	Deployed image and Artifact Registry repo.
monitoring_enabled / monitoring_notification_channels	Monitoring status and channels.
initialization_jobs / db_import_job	Names of the setup and (optional) import jobs.
deployment_id / tenant_id / resource_prefix	Naming identifiers.
project_id / project_number	Project identifiers.
cicd_enabled / cicd_configuration	CI/CD status and details (repo, trigger, registry).
github_repository_url / github_repository_owner / github_repository_name	CI/CD GitHub details.
artifact_registry_repository / cloudbuild_trigger_name / cloudbuild_trigger_id	Registry and build trigger.
kubernetes_ready	Whether the cluster/workload is ready.
vpc_sc_enabled / vpc_sc_perimeter_name / vpc_sc_dry_run_mode	VPC-SC status.
audit_logging_enabled / artifact_registry_cmek_enabled	Audit logging and CMEK status.

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6. Configuration Pitfalls & Sensible Defaults

Risk: Critical (data loss / outage / security) — High (service degraded) — Medium (cost or partial degradation) — Low (minor).

Inherited plan-time validation. This module passes its configuration through the App_GKE foundation engine, which validates values and combinations at plan time — a read replica without its primary, IAP with no authorized identities, a gen1 runtime with NFS/GCS mounts, an out-of-range redis_port/backup_retention_days, ResourceQuota memory without a binary unit suffix. Invalid configuration fails the plan with a clear, named error before any resource is created, so most mistakes below are caught up front rather than at apply or runtime.

Setting	Sensible value	Risk	Consequence if wrong
server_name	Real domain, set once	Critical	Immutable after first boot — changing it invalidates every user ID, device session, and federation relationship.
Signing key persistence (enable_nfs / StatefulSet PVC)	persistent	Critical	If the data directory is not persistent, a pod restart regenerates the signing key, breaking federation and invalidating all device sessions.
Database collation (db-init)	C (automatic)	Critical	Synapse refuses to start against any non-C collation; do not bypass the db-init job.
application_database_name / application_database_user	Set once	Critical	Immutable after first deploy; renaming recreates the DB/user and destroys all data.
enable_backup_import	false unless restoring	Critical	Enabling without a valid backup_uri fails the import job.
container_port / probe port	8008	High	Probes on any other port hit a dead port and the pod never becomes Ready even though Synapse is healthy.
Probe path	/ (default) or /health	High	Pointing a probe at an authenticated Matrix API path returns 401/403 and the pod never becomes Ready.
memory_limit	4Gi (≥ 2 GiB)	High	Below 2 GiB Synapse OOMs under real room/federation load.
min_instance_count	1	High	GKE requires min ≥ 1; keeping 1 ensures the homeserver is always reachable for federation.
session_affinity	ClientIP	High	Without stickiness, a client's requests scatter across pods, disrupting long-lived sync connections.
enable_cloudsql_volume	true	High	The Auth Proxy sidecar is required for PostgreSQL connectivity; disabling it is blocked by a plan-time validation guard.
enable_iap	only for private servers	High	IAP blocks federation and external clients; use only for admin-only deployments.
Rolling update on NFS-backed pods	Recreate (automatic)	High	Two pods against the same data directory + DB can contend; the foundation uses Recreate for NFS-backed apps.
quota_memory_requests / _limits	binary units (4Gi, 8192Mi)	Critical	Bare integers are bytes and block all pod scheduling in the namespace.
enable_pod_disruption_budget	true	Medium	Disabling allows GKE to evict all pods simultaneously during maintenance.
backup_retention_days	7 (raise for prod)	Medium	Too short for compliance retention.

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For the foundation behaviour referenced throughout — IAM and Workload Identity, autoscaling, ingress and certificates, CI/CD, Cloud Armor, IAP, Binary Authorization, VPC-SC, backups, and image mirroring — see App_GKE. Synapse-specific application configuration shared with the Cloud Run variant is described in Synapse_Common.