MongoDB on GKE Autopilot

MongoDB is the world's most popular NoSQL document database, used by organisations of every size for content management, IoT data pipelines, mobile backends, and AI/ML feature stores where relational schemas are too rigid. This module deploys MongoDB on GKE Autopilot on top of the App_GKE foundation, which provisions and manages the shared Google Cloud and Kubernetes infrastructure.

This guide focuses on the cloud services MongoDB uses and how to explore and operate them from the Google Cloud Console and the command line. For the mechanics that are 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

MongoDB runs as a StatefulSet on GKE Autopilot. The deployment wires together a focused set of Google Cloud services:

Capability	Google Cloud service	Notes
Compute	GKE Autopilot (StatefulSet)	1 vCPU / 2 GiB by default, single-node mode
Persistent storage	Persistent Disk (SSD PVC)	standard-rwo StorageClass, 20 GiB default, mounted at /data/db
Secrets	Secret Manager	Auto-generated MongoDB root password
Container images	Artifact Registry	Official mongo image mirrored into the project registry
Networking	VPC / GKE Service	LoadBalancer by default for cross-namespace access; switch to ClusterIP for cluster-internal only

Sensible defaults worth knowing up front:

• No Cloud SQL. MongoDB is its own database engine; Cloud SQL is not provisioned and enable_cloudsql_volume is hardcoded to false.
• SSD-backed PVC is essential. Without a StatefulSet PVC, all data is lost on every pod restart. stateful_pvc_enabled = true auto-selects a StatefulSet.
• Single-node mode only. min_instance_count and max_instance_count are both fixed at 1. MongoDB replica sets require additional authentication-key and rs.initiate() setup that is out of scope for this module.
• Root password is auto-generated. MONGO_INITDB_ROOT_PASSWORD is generated and stored in Secret Manager on the first deploy; you never set it in plain text.
• TCP probes on port 27017. MongoDB speaks its own binary wire protocol, not HTTP — HTTP probes always fail.
• fsGroup 999 is hardcoded. The official MongoDB image runs mongod as UID/GID 999; Kubernetes chowns the PVC mount to this GID automatically.

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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 MongoDB StatefulSet

MongoDB runs as a single-pod StatefulSet on Autopilot, which provisions nodes on demand and bills for the CPU and memory the pod actually requests. Autopilot must provision a node, attach the PVC, and pull the image before mongod starts — the startup probe allows up to ~8 minutes to accommodate this.

• Console: Kubernetes Engine → Workloads → select the MongoDB StatefulSet for pod status, events, and resource usage. Kubernetes Engine → Services & Ingress shows the ClusterIP or external LoadBalancer IP.
• CLI:

  kubectl get statefulset,pods,svc -n "$NAMESPACE"
  kubectl logs -n "$NAMESPACE" statefulset/<statefulset-name> --tail=100
  kubectl describe pod -n "$NAMESPACE" <pod-name>   # events and probe status

See App_GKE for how Autopilot, scaling, and the StatefulSet workload type are managed.

B. Persistent Disk — SSD PVC

MongoDB data lives on a Persistent Disk SSD PVC (standard-rwo StorageClass) mounted at /data/db inside the container. The PVC is provisioned automatically by GKE when the StatefulSet is created and persists independently of pod restarts, rolling updates, and node evictions.

• Console: Kubernetes Engine → Storage → PersistentVolumeClaims to see the PVC and its bound volume. Compute Engine → Disks to see the underlying Persistent Disk.
• CLI:

  kubectl get pvc -n "$NAMESPACE"
  kubectl describe pvc -n "$NAMESPACE" <pvc-name>   # capacity, access mode, status
  # Check disk usage inside the running pod:
  kubectl exec -n "$NAMESPACE" <pod-name> -- df -h /data/db

The PVC size is set at deploy time by stateful_pvc_size (default 20Gi). PVC size cannot be decreased after creation. Provision at least 2–3× the expected initial data volume to avoid the No space left on device crash.

C. Secret Manager — root password

The MongoDB root password (MONGO_INITDB_ROOT_PASSWORD) is auto-generated on the first deploy and stored as a Secret Manager secret. It is injected into the pod via the Secret Store CSI driver and never appears in plain text.

• Console: Security → Secret Manager.
• CLI:

  gcloud secrets list --project "$PROJECT" --filter="name~mongo-root-password"
  gcloud secrets versions access latest \
    --secret=<secret-name> --project "$PROJECT"

To retrieve the root password for a mongosh connection:

ROOT_PASS=$(gcloud secrets versions access latest \
  --secret=<resource-prefix>-mongo-root-password --project "$PROJECT")
kubectl exec -n "$NAMESPACE" <pod-name> -- \
  mongosh --username admin --password "$ROOT_PASS" --authenticationDatabase admin

See App_GKE for the Secret Store CSI integration and rotation.

D. Artifact Registry — container image

The official mongo image is mirrored into the project's Artifact Registry before deployment so pods never pull directly from Docker Hub. The mirrored image URI is reported in the container_image output.

• Console: Artifact Registry → select the repository.
• CLI:

  gcloud artifacts docker images list \
    <region>-docker.pkg.dev/$PROJECT/<registry-repo> --project "$PROJECT"

E. Networking & ingress

By default the MongoDB Kubernetes Service is a LoadBalancer, exposing port 27017 with an external IP so other workloads or developers inside the VPC can reach it. Switch to ClusterIP to restrict access to within the GKE cluster.

• Console: Kubernetes Engine → Services & Ingress; VPC network → IP addresses.
• CLI:

  kubectl get svc -n "$NAMESPACE"
  # Get the LoadBalancer external IP:
  kubectl get svc -n "$NAMESPACE" <service-name> \
    -o jsonpath='{.status.loadBalancer.ingress[0].ip}'

The mongodb_endpoint output provides the ready-to-use connection URI (mongodb://<ip>:27017 for LoadBalancer or the in-cluster DNS URI for ClusterIP).

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

F. Cloud Logging & Monitoring

Pod stdout/stderr (including mongod startup and query logs) flow to Cloud Logging. GKE and Persistent Disk metrics flow to Cloud Monitoring.

• 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. MongoDB Application Behaviour

• Standalone mode only. This module deploys a single mongod instance. MongoDB replica sets (change streams, transactions, oplog replication) require authentication key files and rs.initiate() setup that are outside the scope of this module. max_instance_count is enforced at 1.
• First startup initialisation. On the very first boot with a fresh PVC, MongoDB creates the root user (MONGO_INITDB_ROOT_USERNAME, default admin) and the initial database (MONGO_INITDB_DATABASE, default admin). These values are immutable after the PVC has been written — changing them after first deploy has no effect (the init script runs only once per data directory).
• WiredTiger cache sizing. MongoDB's WiredTiger storage engine defaults its cache to approximately (memory_limit − 1 GiB) × 0.5. With the default 2Gi limit the cache is ~500 MiB, which is sufficient for development. Scale the memory_limit to 4Gi–8Gi for production document workloads.
• Startup probe tolerance. GKE Autopilot must provision a node, attach the PVC, and pull the image before mongod starts. The startup probe allows up to ~8 minutes (failure_threshold = 45, checking every 10 seconds). On subsequent pod restarts on a warm node the startup is much faster.
• Journal flush on shutdown. termination_grace_period_seconds is set to 60 seconds (default) so Kubernetes waits for mongod to flush the write-ahead journal before forcibly killing the process — preventing journal corruption.
• Connection string. The correct format to connect with the root credential is:

  mongodb://<username>:<password>@<host>:<port>/<db>?authSource=admin

  The authSource=admin parameter is required when connecting to non-admin databases with the root account.
• Health probes. Both the startup and liveness probes use type = "TCP" on port 27017. MongoDB speaks its own binary wire protocol — HTTP probes always fail with a protocol error.
• No scheduled tasks. MongoDB does not require any platform-side cron jobs. Application-level tasks (index builds, TTL indices) are managed from within the application or via mongosh.

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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 MongoDB 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	mongodb	Base name for resources. Do not change after first deploy.
application_display_name	MongoDB	Friendly name shown in the Console.
application_description	(set)	Workload description annotation.
application_version	7.0	MongoDB image version tag; increment to roll out a new version. Major upgrades change the on-disk format — test against a replica before upgrading production.
mongo_root_username	admin	Root username (MONGO_INITDB_ROOT_USERNAME). Immutable after first PVC write.
mongo_initdb_database	admin	Initial database created on first startup. Immutable after first PVC write.

Group 4 — Runtime & Scaling

Variable	Default	Description
deploy_application	true	Set false to provision infrastructure only.
cpu_limit	1000m	CPU per pod. Scale to 2000m for aggregation-heavy workloads.
memory_limit	2Gi	Memory per pod. WiredTiger cache ≈ (limit − 1 GiB) × 0.5; scale to 4Gi–8Gi for production.
min_instance_count	1	Minimum replicas. Must be 1 for single-node mode.
max_instance_count	1	Maximum replicas. Enforced at 1 — replica sets are not supported by this module.
container_port	27017	MongoDB wire-protocol port. Sets both the Service port and mongod's listen port.
enable_image_mirroring	true	Mirror the mongo image into Artifact Registry before deployment.
enable_vertical_pod_autoscaling	false	Let Autopilot tune resource requests automatically.

Group 5 — Environment Variables & Secrets

Variable	Default	Description
environment_variables	{}	Extra non-secret settings. MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_DATABASE are injected automatically.
secret_environment_variables	{}	Secret Manager references injected as env vars. Provide MONGO_INITDB_ROOT_PASSWORD here to use a custom password instead of the auto-generated one.
secret_propagation_delay	30	Seconds to wait after the root password secret is created before the pod starts.
secret_rotation_period	2592000s	Secret Manager rotation notification frequency.

Group 6 — GKE Backend & Cluster

Variable	Default	Description
service_type	LoadBalancer	LoadBalancer exposes port 27017 with an external IP; ClusterIP restricts to within the cluster.
workload_type	null	Auto-resolves to StatefulSet when stateful_pvc_enabled = true.
session_affinity	None	No session stickiness required for MongoDB wire-protocol connections.
gke_cluster_name	""	GKE cluster name; leave empty for auto-discovery.
namespace_name	""	Kubernetes namespace; leave empty to auto-generate.
termination_grace_period_seconds	60	Grace period for mongod to flush the journal before SIGKILL.
deployment_timeout	600	Seconds Terraform waits for the StatefulSet rollout (covers node provisioning + PVC attach).
enable_network_segmentation	false	Create Kubernetes NetworkPolicy resources to restrict ingress/egress.

Group 7 — StatefulSet & PVC

Variable	Default	Description
stateful_pvc_enabled	null	Set true to enable PVC-backed StatefulSet. Required for data durability.
stateful_pvc_size	20Gi	Storage size. Cannot be decreased after creation; provision 2–3× expected data volume.
stateful_pvc_mount_path	/data/db	Must match MongoDB's --dbpath. Do not change.
stateful_pvc_storage_class	standard-rwo	GKE Autopilot SSD default. Use premium-rwo for high-throughput workloads.
stateful_headless_service	null	Create a headless Service for stable pod DNS entries.
stateful_pod_management_policy	null	OrderedReady or Parallel pod creation order.
stateful_update_strategy	null	RollingUpdate or OnDelete.
stateful_fs_group	0	fsGroup GID (note: 999 is hardcoded in the module for MongoDB — this variable has no effect).

Group 8 — Resource Quota

Variable	Default	Description
enable_resource_quota	false	Cap namespace CPU/memory/object counts.
quota_memory_requests / quota_memory_limits	""	Must use binary units (4Gi, 8192Mi) — bare integers are read as bytes and block scheduling.

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 disruption (for single-node MongoDB, 1 is the only sensible value).
enable_topology_spread	false	Spread pods across zones.

Group 10 — Observability & Health

Variable	Default	Description
startup_probe_config	TCP, 20s delay, failure_threshold 18	Foundation-level TCP probe input on port 27017. The container's actual startup probe is hardcoded in the module to failure_threshold = 45 (~8 minutes) to cover GKE Autopilot node provisioning + PVC attach + image pull — see Section 3.
health_check_config	TCP, 30s delay, failure_threshold 3	TCP liveness probe on port 27017.
uptime_check_config	disabled	Uptime check — disabled by default as MongoDB is an internal service.
alert_policies	[]	Optional Cloud Monitoring metric alert policies.

Group 11 — Jobs & Scheduled Tasks

Variable	Default	Description
initialization_jobs	[]	Kubernetes Jobs run before the MongoDB pod starts. Not required for MongoDB — no database bootstrap job is needed.
cron_jobs	[]	Scheduled CronJobs. MongoDB has no required platform-side scheduled tasks.

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	false	NFS is not required for MongoDB — use the StatefulSet PVC instead.

Group 14 — Cloud Storage & Artifact Registry

Variable	Default	Description
create_cloud_storage	false	MongoDB does not require a GCS bucket.
manage_storage_kms_iam / enable_artifact_registry_cmek	false	CMEK options for storage and registry.
max_images_to_retain	7	Recent images to keep in Artifact Registry.

Group 17 — Backup & Maintenance

Variable	Default	Description
backup_schedule	0 2 * * *	Automated mongodump backup cron (UTC). Verify the backup job is active — a missed backup combined with PVC deletion causes permanent data loss.
backup_retention_days	7	Retention; raise to 30–90 for production/compliance.

Group 19 — Custom Domain & Static IP

Variable	Default	Description
enable_custom_domain	true	Provisions the Gateway HTTPS ingress (zero-config <ip>.nip.io hostname when application_domains is empty) — unusual for a non-HTTP database service; actual mongodb:// traffic is served by the L4 LoadBalancer Service, not this HTTP(S) ingress.
application_domains	[]	Custom domain names.
reserve_static_ip	true	Stable external IP across redeploys.
network_tags	["nfsserver"]	Node/pod network tags for firewall rules.

Group 20 — Identity-Aware Proxy (IAP)

IAP is not recommended for MongoDB (a database, not a web application). Restrict access instead via service_type = "ClusterIP" or Kubernetes NetworkPolicy.

Variable	Default	Description
enable_iap	false	Not recommended for MongoDB. Use NetworkPolicy or ClusterIP.

Group 21 — Cloud Armor

Variable	Default	Description
enable_cloud_armor	false	Attach a Cloud Armor policy to the Ingress backend.
admin_ip_ranges	[]	CIDRs allowed privileged access.

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 (Cloud Deploy).
service_external_ip	External LoadBalancer IP (when the service type is LoadBalancer).
mongodb_endpoint	Ready-to-use MongoDB connection URI (mongodb://...). ClusterIP deployments return the in-cluster DNS URI; LoadBalancer deployments return the external URI.
statefulset_name	Name of the StatefulSet.
storage_buckets	Created Cloud Storage buckets (empty by default for MongoDB).
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	Names of any initialization jobs run.
deployment_id / tenant_id / resource_prefix	Naming identifiers.
project_id / project_number	Project identifiers.
cicd_enabled / cicd_configuration	CI/CD status and details.
github_repository_url / github_repository_owner / github_repository_name	GitHub repo 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).

Setting	Sensible value	Risk	Consequence if wrong
stateful_pvc_enabled	true	Critical	Without a PVC, all MongoDB data is lost on every pod restart, rolling update, or node eviction.
stateful_pvc_mount_path	/data/db (default)	Critical	Must match MongoDB's --dbpath. Mounting elsewhere causes mongod to write to the ephemeral layer — all data lost on restart.
MONGO_INITDB_ROOT_PASSWORD	auto-generated (default)	Critical	MongoDB starts without authentication if the env var is absent. Any caller inside the cluster gains unrestricted admin access. Never remove or clear it.
mongo_root_username / mongo_initdb_database	set once	Critical	Baked into the data directory on first init. Changing after the PVC exists causes startup failure.
quota_memory_requests / quota_memory_limits	binary units (4Gi)	Critical	Bare integers are read as bytes by Kubernetes, blocking all pod scheduling.
stateful_pvc_size	20Gi min, size for workload	High	A full disk causes mongod to crash with No space left on device. Provision 2–3× expected data volume. Size cannot be decreased after creation.
memory_limit	4Gi for production	High	WiredTiger cache is ~50% of (limit − 1 GiB). Insufficient cache causes excessive disk I/O and severe query degradation.
workload_type	null (auto StatefulSet with PVC)	High	Explicitly setting Deployment alongside stateful_pvc_enabled = true fails at plan time. Standalone MongoDB requires StatefulSet for stable PVC binding.
application_version	test major upgrades first	High	MongoDB major version upgrades change the on-disk storage format. Downgrading is not supported. Always test against a replica of the production PVC.
backup_schedule	active and tested	High	MongoDB has no built-in automatic backup outside this module's mongodump job. A missed backup combined with deletion of the persistent volume on destroy results in permanent data loss.
service_type	ClusterIP for DB-tier services	High	LoadBalancer exposes port 27017 with a public IP. Restrict to ClusterIP unless external access is explicitly required, and use firewall rules or NetworkPolicy.
termination_grace_period_seconds	60 (default)	High	Too short a grace period risks journal corruption on shutdown if in-flight writes have not been flushed.
cpu_limit	2000m for production	Medium	Aggregation pipelines and index builds are CPU-intensive. Below 500m, complex queries degrade significantly.
replica set	standalone only	High	This module is single-node. Change streams, transactions, and oplog replication require a replica set — use a Helm-based deployment for multi-node topologies.
enable_iap	false (default)	Low	IAP is not applicable for database services. Use NetworkPolicy or ClusterIP for access control instead.

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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. MongoDB_GKE has no separate Common module; all MongoDB-specific configuration is self-contained in the module.