Reference: GCP Terminology

A short glossary of Google Cloud terms used in this guide. Equivalents to AWS terms (where relevant) are listed for readers familiar with the AWS GEOS-Chem cloud guide.

Project

What is a GCP Project?

A Project is the top-level GCP container for all resources. Every VM, disk, network, and IP belongs to exactly one project, and billing accumulates per project. Each project is identified by a globally unique Project ID (e.g., gchp-prod-414000), which is what every gcloud command uses.

AWS equivalent: AWS Account.

Compute Engine

What is Compute Engine?

Compute Engine is GCP’s virtual machine service. It hosts the cluster’s controller, login, and burst compute nodes. The two machine types used in this guide are:

c2-standard-60 - Cascade Lake Xeon with 30 physical cores per VM (hyperthreading off). ~$2.48/hour. Good for C48-C90 single-node baseline runs.
h4d-standard-192 - AMD EPYC Bergamo with 192 physical cores per VM and Intel Falcon iRDMA support. ~$10/hour. Required for multi-node Falcon RDMA workloads.

AWS equivalent: EC2.

Cluster Toolkit

What is Cluster Toolkit?

Google’s open-source HPC cluster deployer (formerly called HPC Toolkit). It reads a blueprint (YAML) and generates Terraform code to provision a Slurm cluster on Compute Engine.

Why use Cluster Toolkit for GCHP?

Reproducible: the entire cluster (network, Filestore, partitions, login, controller) is described in one YAML file.
Slurm-integrated: the toolkit configures Slurm-on-GCP, which handles the bursting of compute nodes from the cluster’s pool of zero running nodes when sbatch is invoked, and shuts them down once they have been idle for ~5 minutes.
Cost-aware: only the controller and login VMs are always on. Compute nodes incur charges only while a job is running.

AWS equivalent: AWS ParallelCluster.

Filestore

What is Filestore?

Filestore is GCP’s managed NFS service. We use it for the cluster’s /shared mount holding the Spack stack, GCHP binary, ExtData, and run directories.

The smallest BASIC_HDD volume is 1 TB, costing ~$6.67/day. This is the dominant fixed-cost line for an idle GCHP cluster.

AWS equivalent: FSx for Lustre or EFS.

Slurm (and Slurm-GCP)

What is Slurm?

The standard HPC batch scheduler. Submitted via sbatch, monitored with squeue and sinfo. Cluster Toolkit ships a Slurm-GCP integration that handles burst node provisioning. When you sbatch a job, Slurm-GCP boots the requested number of compute VMs from a pool of cloud-burst nodes (about 90 s for an H4D node), runs the job, then powers them down ~5 minutes after the last job finishes.

Falcon RDMA

What is Falcon RDMA?

Intel’s RDMA-over-Ethernet technology, exposed on H4D instances via the irdma kernel module and a dedicated VPC subnet with a <zone>-vpc-falcon network profile. Gives multi-node MPI the low-latency, zero-copy semantics of InfiniBand.

The supported zones (as of 2026-06) are asia-southeast1-a, europe-west4-b, us-central1-a, us-central1-b, and us-west4-a. The current list can be queried with gcloud compute network-profiles list | grep falcon.

Why Falcon RDMA matters for GCHP

Multi-node MPI via TCP over gVNIC degrades sharply at higher core counts because the kernel network stack adds latency and CPU overhead. Falcon RDMA bypasses the kernel for inter-node communication, restoring near-shared-memory performance across the cluster. Concretely, our C90 strong-scaling stays linear through 360 cores (2 H4D nodes) with Falcon RDMA but would not over TCP.

AWS equivalent: EFA on c5n/hpc6id instances.

gVNIC

What is gVNIC?

Google Virtual NIC - the standard high-performance virtual NIC on modern Compute Engine instances. Carries normal TCP/IP traffic (including NFS to Filestore). On H4D nodes it serves as the primary NIC alongside an IRDMA secondary NIC.

IRDMA NIC

What is an IRDMA NIC?

The NIC type GCP uses for Falcon RDMA on H4D. Attached as a second network interface on each H4D VM, on a Falcon-enabled VPC subnet. The kernel-side driver is the irdma module (loaded automatically at boot by the published GCHP image).

Image

What is a GCP Image?

A snapshot of a VM’s boot disk that can be used to launch new VMs. The gchp-h4d-rocky8-v2 image (this guide) has the kernel modules, system packages, and first-boot scripts required to run GCHP on H4D. See The GCHP compute image and Falcon RDMA for details.

AWS equivalent: AMI.

VPC

What is a VPC on GCP?

Virtual Private Cloud - the networking layer that connects your VMs. Cluster Toolkit creates a regional VPC for the cluster. Falcon RDMA requires a second, zone-pinned VPC with a vpc-falcon network profile.

Service Quota

What is a Service Quota?

A regional or global limit on how many of a particular resource (CPUs, IP addresses, Filestore TB) you can create. Default quotas on a fresh project are low; raise them via IAM & Admin -> Quotas & System Limits.

AWS equivalent: Service Quotas / vCPU limits.

IAM (Identity and Access Management) on GCP

What is IAM on GCP?

Google’s identity and authorization framework. IAM controls who (users, groups, service accounts) can do what (compute.admin, file.editor, etc.) to which resources. Permission grants are made by binding a role (a named set of permissions) to a principal (a user, group, or service account).

When you run terraform apply to deploy a cluster, your user needs roles/compute.admin, roles/file.editor, and several others - listed in Quickstart I: Prepare Your GCP Environment.

Billing Export to BigQuery

What is Billing Export to BigQuery?

A GCP feature that mirrors every billing event into a BigQuery table for SQL analysis. The cleanest way to audit your spend by service over arbitrary time ranges. Enable in Billing -> Billing export.

After 24 hours, you can run queries like:

SELECT service.description, sku.description, SUM(cost) AS usd
FROM `<project>.billing.gcp_billing_export_*`
WHERE invoice.month = FORMAT_DATE('%Y%m', CURRENT_DATE())
GROUP BY 1, 2 ORDER BY usd DESC

Cloud Storage

What is Cloud Storage?

GCP’s object store. Useful for archiving simulation output before tearing down the cluster (terraform destroy) so that destroying Filestore does not lose your results.

AWS equivalent: S3.

Dynamic Workload Scheduler (DWS) Flex Start

What is DWS Flex Start?

A provisioning mode where you ask GCP to run a job “sometime in the next N hours” instead of demanding the resource right now. The scheduler queues your request and starts it when capacity is available. Cheaper than reservations; the right choice for H4D runs that hit ZONE_RESOURCE_POOL_EXHAUSTED stockouts.

Submit with --provisioning-model=FLEX_START on gcloud compute instances bulk create.