Hybrid connectivity network endpoint groups overview

Cloud Load Balancing supports load-balancing traffic to endpoints that extend beyond Google Cloud, such as on-premises data centers and other public clouds that you can use hybrid connectivity to reach.

A hybrid strategy is a pragmatic solution for you to adapt to changing market demands and incrementally modernize your applications. This could be a temporary hybrid deployment to enable migration to a modern cloud-based solution or a permanent fixture of your organization's IT infrastructure.

Setting up hybrid load balancing also lets you bring the benefits of Cloud Load Balancing's networking capabilities to services running on your existing infrastructure outside of Google Cloud.

Hybrid load balancing is supported on the following Google Cloud load balancers:

On-premises and other cloud services are treated like any other Cloud Load Balancing backend. The key difference is that you use a hybrid connectivity NEG to configure the endpoints of these backends. The endpoints must be valid IP:port combinations that your load balancer can reach by using hybrid connectivity products such as Cloud VPN or Cloud Interconnect.

Use-case: Routing traffic to an on-premises location or another cloud

The simplest use case for using hybrid NEGs is routing traffic from a Google Cloud load balancer to an on-premises location or to another cloud environment. Clients can originate traffic either from the public internet, from within Google Cloud, or from an on-premises client.

Public clients

You can use an external Application Load Balancer with a hybrid NEG backend to route traffic from external clients to a backend on-premises or in another cloud network. You can also enable the following value-added networking capabilities for your services on-premises or in other cloud networks:

  • With the global external Application Load Balancer and classic Application Load Balancer, you can:

    • Use Google's global edge infrastructure to terminate user connections closer to the user, thus decreasing latency.
    • Protect your service with Google Cloud Armor, an edge DDoS defense/WAF security product available to all services accessed through an external Application Load Balancer.
    • Enable your service to optimize delivery using Cloud CDN. With Cloud CDN, you can cache content close to your users. Cloud CDN provides capabilities like cache invalidation and Cloud CDN signed URLs.
    • Use Google-managed SSL certificates. You can reuse certificates and private keys that you already use for other Google Cloud products. This eliminates the need to manage separate certificates.

    The following diagram demonstrates a hybrid deployment with an external Application Load Balancer.

    Hybrid connectivity with a global external Application Load Balancer.
    Hybrid connectivity with a global external Application Load Balancer (click to enlarge).

    In this diagram, traffic from clients on the public internet enters your private on-premise or cloud network through a Google Cloud load balancer, such as the external Application Load Balancer. When traffic reaches the load balancer, you can apply network edge services such as Google Cloud Armor DDoS protection or Identity-Aware Proxy (IAP) user authentication.

  • With the regional external Application Load Balancer, you can route external traffic to endpoints that are within the same Google Cloud region as the load balancer's resources. Use this load balancer if you need to serve content from only one geolocation (for example, to meet compliance regulations) or if the Standard Network Service Tier is desired.

How the request is routed (whether to a Google Cloud backend or to an on-premises/cloud endpoint) depends on how your URL map is configured. Depending on your URL map, the load balancer selects a backend service for the request. If the selected backend service has been configured with a hybrid connectivity NEG (used for non-Google Cloud endpoints only), the load balancer forwards the traffic across Cloud VPN or Cloud Interconnect to its intended external destination.

Internal clients (within Google Cloud or on-premises)

You can also set up a hybrid deployment for clients internal to Google Cloud. In this case, client traffic originates from the Google Cloud VPC network, your on-premises network, or from another cloud, and is routed to endpoints on-premises or in other cloud networks.

The regional internal Application Load Balancer is a regional load balancer, which means that it can only route traffic to endpoints within the same Google Cloud region as the load balancer's resources. The cross-region internal Application Load Balancer is a multi-region load balancer that can load balance traffic to backend services that are globally distributed.

The following diagram demonstrates a hybrid deployment with a regional internal Application Load Balancer.

Hybrid connectivity with regional internal Application Load Balancers.
Hybrid connectivity with regional internal Application Load Balancers (click to enlarge).

Use-case: Migrate to Cloud

Migrating an existing service to cloud enables you to free up on-premise capacity and reduce the cost and burden of maintaining on-premise infrastructure. You can temporarily set up a hybrid deployment that allows you to route traffic to both your current on-premises service and a corresponding Google Cloud service endpoint.

The following diagram demonstrates this setup with an internal Application Load Balancer.
Migrate to Google Cloud.
Migrate to Google Cloud (click to enlarge).

If you are using an internal Application Load Balancer to handle internal clients, you can configure the Google Cloud load balancer to use weight-based traffic splitting to split traffic across the two services. Traffic splitting lets you start by sending 0% of traffic to the Google Cloud service and 100% to the on-premises service. You can then gradually increase the proportion of traffic sent to the Google Cloud service. Eventually, you send 100% of traffic to the Google Cloud service, and you can retire the on-premises service.

Hybrid architecture

This section describes the load balancing architecture and resources required to configure a hybrid load balancing deployment.

On-premises and other cloud services are like any other Cloud Load Balancing backend. The key difference is that you use a hybrid connectivity NEG to configure the endpoints of these backends. The endpoints must be valid IP:port combinations that your clients can reach through hybrid connectivity, such as Cloud VPN or Cloud Interconnect.

The following diagrams show the Google Cloud resources required to enable hybrid load balancing for external Application Load Balancers and regional internal Application Load Balancers.

Global external HTTP(S)

Global external Application Load Balancer resources for hybrid connectivity.
Global external Application Load Balancer resources for hybrid connectivity (click to enlarge).

Regional external HTTP(S)

Regional external Application Load Balancer resources for hybrid connectivity.
Regional external Application Load Balancer resources for hybrid connectivity (click to enlarge).

Regional internal HTTP(S)

Regional internal Application Load Balancer resources for hybrid connectivity.
Regional internal Application Load Balancer resources for hybrid connectivity (click to enlarge).

Regional internal proxy

Regional internal proxy Network Load Balancer resources for hybrid connectivity.
Regional internal proxy Network Load Balancer resources for hybrid connectivity (click to enlarge).

Regional versus global

Cloud Load Balancing routing depends on the scope of the configured load balancer:

External Application Load Balancer and external proxy Network Load Balancer. These load balancers can be configured for either global or regional routing depending on the network tier that is used. You create the load balancer's hybrid NEG backend in the same network and region where hybrid connectivity has been configured. Non-Google Cloud endpoints must also be configured accordingly to take advantage of proximity-based load balancing.

Cross-region internal Application Load Balancer and cross-region internal proxy Network Load Balancer. This is a multi-region load balancer that can load balance traffic to backend services that are globally distributed. You create the load balancer's hybrid NEG backend in the same network and region where hybrid connectivity has been configured. Non-Google Cloud endpoints must also be configured accordingly to take advantage of proximity-based load balancing.

Regional internal Application Load Balancer and regional internal proxy Network Load Balancer. These are regional load balancers. That is, they can only route traffic to endpoints within the same region as the load balancer. The load balancer components must be configured in the same region where hybrid connectivity has been configured. By default, clients accessing the load balancer must also be in the same region. However, if you enable global access, clients from any region can access the load balancer.

For example, if the Cloud VPN gateway or the Cloud Interconnect VLAN attachment is configured in REGION_A, the resources required by the load balancer (such as a backend service, hybrid NEG, or forwarding rule) must be created in the REGION_A region. By default, clients accessing the load balancer must also be in the REGION_A region. However, if you enable global access, clients from any region can access the load balancer.

Network connectivity requirements

Before you configure a hybrid load balancing deployment, you must have the following resources set up:

  • Google Cloud VPC network. A VPC network configured inside Google Cloud. This is the VPC network used to configure Cloud Interconnect/Cloud VPN and Cloud Router. This is also the same network where you'll create the load balancing resources (forwarding rule, target proxy, backend service, etc.). On-premises, other cloud, and Google Cloud subnet IP addresses and IP address ranges must not overlap. When IP addresses overlap, subnet routes are prioritized over remote connectivity.

  • Hybrid connectivity. Your Google Cloud and on-premises or other cloud environments must be connected through hybrid connectivity, using either Cloud Interconnect VLAN attachments or Cloud VPN tunnels with Cloud Router. We recommend that you use a high availability connection. A Cloud Router enabled with global dynamic routing learns about the specific endpoint via BGP and programs it into your Google Cloud VPC network. Regional dynamic routing is not supported. Static routes are also not supported.

    Cloud Interconnect/Cloud VPN and Cloud Router must be configured in the same VPC network that you intend to use for the hybrid load balancing deployment. The Cloud Router must also advertise the following routes to your on-premises environment:

    • Ranges used by Google's health check probes: 35.191.0.0/16 and 130.211.0.0/22. This is required for global external Application Load Balancers, classic Application Load Balancers, global external proxy Network Load Balancers, and classic proxy Network Load Balancers.

    • The range of the region's proxy-only subnet: for Envoy-based load balancers—regional external Application Load Balancers, regional internal Application Load Balancers, cross-region internal Application Load Balancers, regional external proxy Network Load Balancers, cross-region internal proxy Network Load Balancers, and regional internal proxy Network Load Balancers.

      Advertising region's proxy-only subnet is also required for distributed Envoy health checks to work. Distributed Envoy health check is the default health check mechanism for zonal hybrid connectivity NEGS (that is, NON_GCP_PRIVATE_IP_PORT endpoints) behind Envoy-based load balancers.

  • Network endpoints (IP:Port) on-premises or in other clouds. One or more IP:Port network endpoints configured within your on-premises or other cloud environments, routable using Cloud Interconnect or Cloud VPN. If there are multiple paths to the IP endpoint, routing will follow the behavior described in the VPC routes overview and the Cloud Router overview.

  • Firewall rules on your on-premises or other cloud. The following firewall rules must be created on your on-premises or other cloud environment:

    • Ingress allow firewall rules to allow traffic from Google's health-checking probes to your endpoints. The ranges to be allowed are: 35.191.0.0/16 and 130.211.0.0/22. Note that these ranges must also be advertised by Cloud Router to your on-premises network. For more details, see Probe IP ranges and firewall rules.
    • Ingress allow firewall rules to allow traffic that is being load-balanced to reach the endpoints.
    • For Envoy-based load balancers—regional external Application Load Balancers, regional internal Application Load Balancers, cross-region internal Application Load Balancers, regional external proxy Network Load Balancers, cross-region internal proxy Network Load Balancer, and regional internal proxy Network Load Balancers, you also need to create a firewall rule to allow traffic from the region's proxy-only subnet to reach the endpoints that are on-premises or in other cloud environments.

Load balancer components

Depending on the type of load balancer, you can set up a hybrid load-balancing deployment by using either the Standard or the Premium Network Service Tiers.

A hybrid load balancer requires special configuration only for the backend service. The frontend configuration is the same as any other load balancer. The Envoy-based load balancers—regional external Application Load Balancers, regional internal Application Load Balancers, cross-region internal Application Load Balancers, regional external proxy Network Load Balancers, cross-region internal proxy Network Load Balancer, and regional internal proxy Network Load Balancers,—require an additional proxy-only subnet to run Envoy proxies on your behalf.

Frontend configuration

No special frontend configuration is required for hybrid load balancing. Forwarding rules are used to route traffic by IP address, port, and protocol to a target proxy. The target proxy then terminates connections from clients.

URL maps are used by HTTP(S) load balancers to set up URL-based routing of requests to the appropriate backend services.

For more details on each of these components, refer the architecture sections of the specific load balancer overviews:

Backend service

Backend services provide configuration information to the load balancer. Load balancers use the information in a backend service to direct incoming traffic to one or more attached backends.

To set up a hybrid load balancing deployment, you configure the load balancer with backends that are both within Google Cloud, as well as outside of Google Cloud.

  • Non-Google Cloud backends (on-premise or other cloud)

    Any destination that you can reach using Google's hybrid connectivity products (either Cloud VPN or Cloud Interconnect), and that can be reached with a valid IP:Port combination, can be configured as an endpoint for the load balancer.

    Configure your non-Google Cloud backends as follows:

    1. Add each non-Google Cloud network endpoint's IP:Port combination to a hybrid connectivity network endpoint group (NEG). Make sure this IP address and port is reachable from Google Cloud by using hybrid connectivity (either by Cloud VPN or Cloud Interconnect). For hybrid connectivity NEGs, you set the network endpoint type to NON_GCP_PRIVATE_IP_PORT.
    2. While creating the NEG, specify a Google Cloud zone that minimizes the geographic distance between Google Cloud and your on-premises or other cloud environment. For example, if you are hosting a service in an on-premises environment in Frankfurt, Germany, you can specify the europe-west3-a Google Cloud zone when you create the NEG.

    3. Add this hybrid connectivity NEG as a backend for the backend service.

      A hybrid connectivity NEG must only include non-Google Cloud endpoints. Traffic might be dropped if a hybrid NEG includes endpoints for resources within a Google Cloud VPC network, such as forwarding rule IP addresses for internal passthrough Network Load Balancers. Configure Google Cloud endpoints as directed in the next section.

  • Google Cloud backends

    Configure your Google Cloud endpoints as follows:

    1. Create a separate backend service for the Google Cloud backends.
    2. Configure multiple backends (either GCE_VM_IP_PORT zonal NEGs or instance groups) within the same region in which you have set up hybrid connectivity.

Additional points for consideration:

  • Each hybrid connectivity NEG can only contain network endpoints of the same type (NON_GCP_PRIVATE_IP_PORT).

  • You can use a single backend service to reference both Google Cloud-based backends (using zonal NEGs with GCE_VM_IP_PORT endpoints) and on-premises or other cloud backends (using hybrid connectivity NEGs with NON_GCP_PRIVATE_IP_PORT endpoints). No other combination of mixed backend types is allowed. Cloud Service Mesh does not support mixed backend types in a single backend service.

  • The backend service's load balancing scheme must be one of the following:

    • EXTERNAL_MANAGED for global external Application Load Balancers, regional external Application Load Balancers, global external proxy Network Load Balancers, and regional external proxy Network Load Balancers

    • EXTERNAL for classic Application Load Balancers and classic proxy Network Load Balancers

    • INTERNAL_MANAGED for internal Application Load Balancers and Internal proxy Network Load Balancers

    INTERNAL_SELF_MANAGED is supported for Cloud Service Mesh multi-environment deployments with hybrid connectivity NEGs.

  • The backend service protocol must be one of HTTP, HTTPS, or HTTP2 for the Application Load Balancers, and either TCP or SSL for the proxy Network Load Balancers. For the list of backend service protocols supported by each load balancer, see Protocols from the load balancer to the backend.

  • The balancing mode for the hybrid NEG backend must be RATE for Application Load Balancers, and CONNECTION for proxy Network Load Balancers. For details on balancing modes, see Backend services overview.

  • To add more network endpoints, update the backends attached to your backend service.

  • If you're using distributed Envoy health checks with hybrid connectivity NEG backends (supported only for Envoy-based load balancers), make sure that you configure unique network endpoints for all the NEGs attached to the same backend service. Adding the same network endpoint to multiple NEGs results in undefined behavior.

Centralized health checks

Centralized health checks, when using hybrid NEGs, are required for global external Application Load Balancers, classic Application Load Balancers, global external proxy Network Load Balancers, and classic proxy Network Load Balancers. Other Envoy-based load balancers use distributed Envoy health checks as described in the following section.

For NON_GCP_PRIVATE_IP_PORT endpoints outside Google Cloud, create firewall rules on your on-premises and other cloud networks. Contact your network administrator for this. The Cloud Router used for hybrid connectivity must also advertise the ranges used by Google's health check probes. The ranges to be advertised are 35.191.0.0/16 and 130.211.0.0/22.

For other types of backends within Google Cloud, create firewall rules on Google Cloud as demonstrated in this example.

Related documentation:

Distributed Envoy health checks

Your health check configuration varies depending on the type of load balancer:

  • Global external Application Load Balancer, classic Application Load Balancer, global external proxy Network Load Balancer , and classic proxy Network Load Balancer. These load balancers don't support distributed Envoy health checks. They use Google's centralized health checking mechanism as described in the section Centralized health checks.

  • Regional external Application Load Balancer, regional internal Application Load Balancer, regional external proxy Network Load Balancer, regional internal proxy Network Load Balancer , cross-region internal proxy Network Load Balancer, and cross-region internal Application Load Balancer. These load balancers use distributed Envoy health checks to check the health of hybrid NEGs. The health check probes originate from the Envoy proxy software itself. Each backend service must be associated with a health check that checks the health of the backends. Health check probes originate from the Envoy proxies in the proxy-only subnet in the region. For the health check probes to function correctly, you must create firewall rules in the external environment that allow traffic from the proxy-only subnet to reach your external backends.

    For NON_GCP_PRIVATE_IP_PORT endpoints outside Google Cloud, you must create these firewall rules on your on-premises and other cloud networks. Contact your network administrator for this. The Cloud Router that you use for hybrid connectivity must also advertise the region's proxy-only subnet range.

Distributed Envoy health checks are created by using the same Google Cloud console, gcloud CLI, and API processes as centralized health checks. No other configuration is required.

Points to note:

  • gRPC health checks are not supported.
  • Health checks with PROXY protocol v1 enabled are not supported.
  • If you use mixed NEGs where a single backend service has a combination of zonal NEGs (GCE_VM_IP_PORT endpoints within Google Cloud) and hybrid NEGs (NON_GCP_PRIVATE_IP_PORT endpoints outside Google Cloud), you need to set up firewall rules to allow traffic from Google health check probe IP ranges (130.211.0.0/22 and 35.191.0.0/16) to the zonal NEG endpoints on Google Cloud. This is because zonal NEGs use Google's centralized health checking system.

  • Because the Envoy data plane handles health checks, you cannot use the Google Cloud console, the API, or the gcloud CLI to check the health status of these external endpoints. For hybrid NEGs with Envoy-based load balancers, the Google Cloud console shows the health check status as N/A. This is expected.

  • Every Envoy proxy assigned to the proxy-only subnet in the region in the VPC network initiates health checks independently. Therefore, you might see an increase in network traffic because of health checking. The increase depends on the number of Envoy proxies assigned to your VPC network in a region, the amount of traffic received by these proxies, and the number of endpoints that each Envoy proxy needs to health check. In the worst case scenario, network traffic because of health checks increases at a quadratic (O(n^2)) rate.

  • Health check logs for distributed Envoy health checks don't include detailed health states. For details about what is logged, see Health check logging. To further troubleshoot connectivity from Envoy proxies to your NEG endpoints, you should also check the respective load balancer logs.

Related documentation:

Limitations

  • The Cloud Router used for hybrid connectivity must be enabled with global dynamic routing. Regional dynamic routing and static routes are not supported.
  • For the Envoy-based regional load balancers—regional external Application Load Balancers, regional external proxy Network Load Balancers, regional internal proxy Network Load Balancers, and regional internal Application Load Balancers—hybrid connectivity must be configured in the same region as the load balancer. If they are configured in different regions, you might see backends as healthy but client requests will not be forwarded to the backends.

  • The considerations for encrypted connections from the load balancer to the backends documented here also apply to non-Google Cloud backend endpoints configured in the hybrid connectivity NEG.

    Make sure that you also review the security settings on your hybrid connectivity configuration. Currently, HA VPN connections are encrypted by default (IPsec). Cloud Interconnect connections are not encrypted by default. For more details, see the Encryption in transit whitepaper.

Logging

Requests proxied to an endpoint in a hybrid NEG are logged to Cloud Logging in the same way that requests for other backends are logged. If you enable Cloud CDN for your global external Application Load Balancer, cache hits are also logged.

For more information, see:

Quota

You can configure as many hybrid NEGs with network endpoints as permitted by your existing network endpoint group quota. For more information, see NEG backends and Endpoints per NEG.

What's next