GCP PSC Dynamic Port Allocation
Parent: MongoDB Atlas on GCP · Published reference · snapshot 2026-10-29
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Source-anchored research for GCP PSC Dynamic Port Allocation. Run status: COMPLETED.
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How it works
- For GCP-only multi-region migration, Atlas says port-mapped connection strings require a port-mapped endpoint service in every cluster region, except when regionalized private endpoints apply. For multi-cloud clusters with both architectures in a region, Atlas requires deleting the legacy service before connecting through the port-mapped service; the generic parallel-migration recipe needs this qualification. (low confidence) (verified as of 2026-10-29) [source]
Problems, failure modes and limitations
- Atlas GCP PSC endpoints use destination ports 1024–65535, and assignments can change during cluster changes. A firewall rule or client configuration that assumes a permanent node port can therefore lose connectivity; this is a documented failure mechanism, not evidence of a specific customer incident. (medium confidence) (verified as of 2026-10-29) [source]
- Enable port mapping explicitly with Atlas portMappingEnabled=true or Terraform port_mapping_enabled=true. Atlas migration creates a new endpoint resource, moves applications to its generated connection string, verifies connectivity, and then removes legacy resources. The Terraform guide says an existing mongodbatlas_privatelink_endpoint cannot be modified in place to enable port mapping. (medium confidence) (verified as of 2026-10-29) [source]
Comparisons and alternatives
- MongoDB recommends the DNS seedlist private endpoint-aware connection string (mongodb+srv) so DNS reflects changed GCP PSC ports, and recommends allowing the entire endpoint port range rather than selected ports. Its troubleshooting guide scopes outbound access to the forwarding rules' private IP addresses. (medium confidence) (verified as of 2026-10-29) [source]
- A GCP-only port-mapped connection string generally uses psc-[index] instead of the legacy pl-[index]. Multi-cloud clusters retain the pl-[index] pattern, so generating connection strings by a universal hostname substitution is unsafe; retrieve the actual Atlas-generated string. (medium confidence) (verified as of 2026-10-29) [source]
- Google’s generic PSC port-mapping service forwards traffic according to producer-defined mappings rather than balancing across healthy backends. Producers must communicate valid destination mappings to consumers; PSC does not distribute them automatically. (low confidence) [source]
Facts and statements
- For diagnosis, query the private-endpoint hostname with nslookup -type=SRV and test connectivity to the returned hostname and port from the application environment. The GCP example returns distinct node ports 1024, 1025 and 1026. (low confidence) [source]
- PSC port mapping selects a particular producer VM and service port from the consumer destination port. Atlas applies this model to expose multiple nodes through a single customer IP address, decoupling node count from customer IP count. (medium confidence) [source]
- MongoDB’s Terraform migration guide describes a port-mapped service attachment supporting up to 150 nodes with one Compute Address and one forwarding rule, replacing the legacy per-node resource pattern. (low confidence) (verified as of 2026-10-29) [source]
- The label 'GCP PSC Dynamic Port Allocation' must be scoped: Google's Cloud NAT dynamic port allocation changes a VM's allocation of NAT source IP/port tuples with demand, whereas PSC port mapping routes client destination ports to producer VM/service-port pairs. The Cloud NAT setting is not documented here as an Atlas PSC destination-port control. (medium confidence) [source]
- Current Atlas overview and troubleshooting pages announce that non-port-mapped GCP endpoints will be disabled on April 30, 2027 and existing endpoints will stop working. This is the published schedule verified on October 29, 2026; older migration guidance still says migration is optional. (medium confidence) (verified as of 2026-10-29) [source]
- Pulumi's PrivateLinkEndpoint API exposes the GCP-only portMappingEnabled input; its documented false or unset behavior selects the legacy architecture. The Pulumi package explicitly derives from the MongoDB Atlas Terraform provider, so this is evidence of Pulumi's interface, not independent corroboration of Atlas backend behavior. (low confidence) (verified as of 2026-10-27) [source]
- Fivetran's MongoDB replica-set setup guide documents Atlas private-network setup for AWS PrivateLink and Azure Private Link, while its GCP private-network instructions refer to MongoDB hosted on VMs. The inspected guide does not establish an Atlas GCP PSC port-mapped workflow; confirm connector compatibility before relying on it. (low confidence) (verified as of 2026-10-29) [source]
Children
- GCP PSC destination-port changes and SRV discovery (frontier)
- Port-mapped endpoint migration constraints (frontier)
- Atlas GCP PSC DNS seedlist discovery (frontier)
- GCP PSC firewall egress ranges (frontier)
- Legacy-to-port-mapped endpoint migration (frontier)
Frontier under this node: Atlas GCP PSC DNS seedlist discovery, GCP PSC destination-port changes and SRV discovery, GCP PSC firewall egress ranges, Legacy-to-port-mapped endpoint migration, Port-mapped endpoint migration constraints