Internal passthrough Network Load Balancer overview

An internal passthrough Network Load Balancer is a regional load balancer that is built on the Andromeda network virtualization stack.

Internal passthrough Network Load Balancers distribute traffic among internal virtual machine (VM) instances in the same region in a Virtual Private Cloud (VPC) network. It enables you to run and scale your services behind an internal IP address that is accessible only to systems in the same VPC network or systems connected to your VPC network.

Use an internal passthrough Network Load Balancer in the following circumstances:

  • You need a high-performance, pass-through Layer 4 load balancer for TCP, UDP, ICMP, ICMPv6, SCTP, ESP, AH, and GRE protocols.
  • If serving traffic through TLS (SSL), it is acceptable to have SSL traffic terminated by your backends instead of by the load balancer. The internal passthrough Network Load Balancer cannot terminate SSL traffic.
  • You need to forward the original packets unproxied. For example, if you need the client source IP address to be preserved.
  • You have an existing setup that uses a pass-through load balancer, and you want to migrate it without changes.

The internal passthrough Network Load Balancers address many use cases. For a few high-level examples, see Passthrough Network Load Balancer overview.

How internal passthrough Network Load Balancers work

An internal passthrough Network Load Balancer has a frontend (the forwarding rule) and a backend (the backend service). You can use either instance groups or GCE_VM_IP zonal NEGs as backends on the backend service. This example shows instance group backends.

High-level internal passthrough Network Load Balancer example.
High-level internal passthrough Network Load Balancer example (click to enlarge).

Unlike a proxy load balancer, an internal passthrough Network Load Balancer doesn't terminate connections from clients and then open new connections to backends. Instead, an internal passthrough Network Load Balancer routes connections directly from clients to the healthy backends, without any interruption. Responses from the healthy backend VMs go directly to the clients, not back through the load balancer. TCP responses use direct server return. For more information, see TCP and UDP request and return packets.

The load balancer monitors backend health by using health check probes. For more information, see the Health check section.

The Google Cloud Linux guest environment, Windows guest environment, or an equivalent process configures each backend VM with the IP address of the load balancer. For VMs created from Google Cloud images, the Guest agent (formerly, the Windows Guest Environment or Linux Guest Environment) installs the local route for the load balancer's IP address. Google Kubernetes Engine instances based on Container- Optimized OS implement this by using iptables instead.

Google Cloud virtual networking manages traffic delivery and scaling as appropriate.

Protocols, scheme, and scope

Each internal passthrough Network Load Balancer supports the following:

  • One backend service with load balancing scheme INTERNAL and a supported protocol. For more information, see backend service.
  • Backend VMs specified as either one of the following:
  • Support for IPv4 and IPv6 traffic when using instance group backends. Zonal network endpoint groups (NEGs) with GCE_VM_IP endpoints only support IPv4 traffic.
  • One or more forwarding rules, each using either the TCP, UDP, or L3_DEFAULT protocol matching the backend service's protocol.
  • Each forwarding rule with its own unique IP address or multiple forwarding rules that share a common IP address.
  • Each forwarding rule with up to five ports or all ports.
  • If global access is enabled, clients in any region.
  • If global access is disabled, clients in the same region as the load balancer.

An internal passthrough Network Load Balancer doesn't support:

Client access

By default, the load balancer only supports clients that are in the same region as the load balancer. Clients can be in the same network as the load balancer or in a VPC network connected by using VPC Network Peering. You can enable global access to allow clients from any region to access your internal passthrough Network Load Balancer.

Internal passthrough Network Load Balancer with global access.
Internal passthrough Network Load Balancer with global access (click to enlarge).

The following table summarizes client access.

Global access disabled Global access enabled
Clients must be in the same region as the load balancer. They also must be in the same VPC network as the load balancer or in a VPC network that is connected to the load balancer's VPC network by using VPC Network Peering. Clients can be in any region. They still must be in the same VPC network as the load balancer or in a VPC network that's connected to the load balancer's VPC network by using VPC Network Peering.
On-premises clients can access the load balancer through Cloud VPN tunnels or VLAN attachments. These tunnels or attachments must be in the same region as the load balancer. On-premises clients can access the load balancer through Cloud VPN tunnels or VLAN attachments. These tunnels or attachments can be in any region.

IP addresses for request and return packets

When a backend VM receives a load-balanced packet from a client, the packet's source and destination are:

  • Source: the client's internal IPv4, IPv6, or the IPv4 address from one of the client's alias IPv4 ranges.
  • Destination: the IP address of the load balancer's forwarding rule. The forwarding rule uses either a single internal IPv4 address or an internal IPv6 range.

Because the load balancer is a pass-through load balancer (not a proxy), packets arrive bearing the destination IP address of the load balancer's forwarding rule. Software running on backend VMs should be configured to do the following:

  • Listen on (bind to) the load balancer's forwarding rule IP address or any IP address (0.0.0.0 or ::)
  • If the load balancer forwarding rule's protocol supports ports: Listen on (bind to) a port that's included in the load balancer's forwarding rule

Return packets are sent directly from the load balancer's backend VMs to the client. The return packet's source and destination IP addresses depend on the protocol:

  • TCP is connection-oriented so backend VMs must reply with packets whose source IP addresses match the forwarding rule's IP address so that the client can associate the response packets with the appropriate TCP connection.
  • UDP is connectionless so backend VMs can send response packets whose source IP addresses either match the forwarding rule's IP address or match any assigned IP address for the VM. Practically speaking, most clients expect the response to come from the same IP address to which they sent packets.

The following table summarizes sources and destinations for response packets:

Traffic type Source Destination
TCP The IP address of the load balancer's forwarding rule The requesting packet's source
UDP For most use cases, the IP address of the load balancer's forwarding rule † The requesting packet's source

† It is possible to set the response packet's source to the VM NIC's primary internal IPv4 address or an alias IP address range. If the VM has IP forwarding enabled, arbitrary IP address sources can also be used. Not using the forwarding rule's IP address as a source is an advanced scenario because the client receives a response packet from an internal IP address that does not match the IP address to which it sent a request packet.

Architecture

An internal passthrough Network Load Balancer with multiple backends distributes connections among all of those backends. For information about the distribution method and its configuration options, see traffic distribution.

You can use either instance groups or zonal NEGs, but not a combination of both, as backends for an internal passthrough Network Load Balancer:

  • If you choose instance groups, you can use unmanaged instance groups, zonal managed instance groups, regional managed instance groups, or a combination of instance group types.
  • If you choose zonal NEGs, you must use GCE_VM_IP zonal NEGs.

High availability describes how to design an internal load balancer that is not dependent on a single zone.

Instances that participate as backend VMs for internal passthrough Network Load Balancers must be running the appropriate Linux or Windows guest environment or other processes that provide equivalent functionality. This guest environment must be able to contact the metadata server (metadata.google.internal, 169.254.169.254) to read instance metadata so that it can generate local routes to accept traffic sent to the load balancer's internal IP address.

This diagram illustrates traffic distribution among VMs located in two separate instance groups. Traffic sent from the client instance to the IP address of the load balancer (10.10.10.9) is distributed among backend VMs in either instance group. Responses sent from any of the serving backend VMs are delivered directly to the client VM.

You can use an internal passthrough Network Load Balancer with either a custom mode or auto mode VPC network. You can also create internal passthrough Network Load Balancers with an existing legacy network.

An internal passthrough Network Load Balancer consists of the following Google Cloud components.

Component Purpose Requirements
Internal IP address This is the address for the load balancer. The internal IP address must be in the same subnet as the internal forwarding rule. The subnet must be in the same region and VPC network as the backend service.
Internal forwarding rule An internal forwarding rule in combination with the internal IP address is the frontend of the load balancer. It defines the protocol and port(s) that the load balancer accepts, and it directs traffic to a regional internal backend service. Forwarding rules for internal passthrough Network Load Balancers must do the following:
• Have a load-balancing-scheme of INTERNAL.
• Use an ip-protocol of either TCP or UDP, matching the protocol of the backend service.
• Reference a subnet in the same VPC network and region as the backend service.
Regional internal backend service The regional internal backend service defines the protocol used to communicate with the backends, and it specifies a health check. Backends can be unmanaged instance groups, managed zonal instance groups, managed regional instance groups, or zonal NEGs with GCE_VM_IP endpoints. The backend service must do the following:
• Have a load-balancing-scheme of INTERNAL.
• Use a protocol of either TCP or UDP, matching the ip-protocol of the forwarding rule.
• Have an associated health check.
• Have an associated region. The forwarding rule and all backends must be in the same region as the backend service
• Be associated with a single VPC network. When not specified, the network is inferred based on the network used by each backend VM's default network interface (nic0).

Although the backend service is not tied to a specific subnet, the forwarding rule's subnet must be in the same VPC network as the backend service.
Health check Every backend service must have an associated health check. The health check defines the parameters under which Google Cloud considers the backends that it manages to be eligible to receive traffic. Only healthy backend VMs receive traffic sent from client VMs to the IP address of the load balancer.
 Even though the forwarding rule and backend service can use either TCP or UDP, Google Cloud does not have a health check for UDP traffic. For more information, see health checks and UDP traffic.

An internal passthrough Network Load Balancer doesn't support:

Internal IP address

Internal passthrough Network Load Balancers support IPv4-only, dual-stack, and IPv6-only subnets. For more information about each one, see Types of subnets.

An internal passthrough Network Load Balancer requires at least one forwarding rule. The forwarding rule references the internal IP address:

  • For IPv4 traffic, the forwarding rule references an IPv4 address from the primary IPv4 subnet range.

  • For IPv6 traffic, the forwarding rule references a /96 range of internal IPv6 addresses from the subnet's /64 internal IPv6 address range. The subnet must be either a dual-stack or single-stack IPv6-only (Preview) subnet with an internal IPv6 address range (ipv6-access-type set to INTERNAL). The IPv6 address range can be a reserved static address or an ephemeral address.

    For more information about IPv6 support, see the VPC documentation about IPv6 subnet ranges and IPv6 addresses.

Firewall configuration

Internal passthrough Network Load Balancers require the following configuration for hierarchical firewall policies and VPC firewall rules:

For more information, see Configuring firewall rules.

Forwarding rules

A forwarding rule specifies the protocol and ports on which the load balancer accepts traffic. Because internal passthrough Network Load Balancers are not proxies, they pass traffic to backends on the same protocol and port.

An internal passthrough Network Load Balancer requires at least one internal forwarding rule. You can define multiple forwarding rules for the same load balancer.

If you want the load balancer to handle both IPv4 and IPv6 traffic, create two forwarding rules: one rule for IPv4 traffic that points to IPv4 (or dual-stack) backends, and one rule for IPv6 traffic that points only to dual-stack backends. It's possible to have an IPv4 and an IPv6 forwarding rule reference the same backend service, but the backend service must reference dual-stack backends.

The forwarding rule must reference a specific subnet in the same VPC network and region as the load balancer's backend components. This requirement has the following implications:

  • The subnet that you specify for the forwarding rule doesn't need to be the same as any of the subnets used by backend VMs; however, the subnet must be in the same region as the forwarding rule.
  • For IPv4 traffic, the internal forwarding rule references regional internal IPv4 address from the primary IPv4 address range of the subnet that you select. This IPv4 address can be selected automatically or you can use a static (reserved) IPv4 address.
  • For IPv6 traffic, the forwarding rule references a /96 range of IPv6 addresses from the subnet's /64 internal IPv6 address range. The subnet must be a dual-stack subnet with the ipv6-access-type set to INTERNAL. The /96 IPv6 address range is either assigned automatically or you can use a reserved internal IP address.

Forwarding rule protocols

Internal passthrough Network Load Balancers support the following IPv4 protocol options for each forwarding rule: TCP, UDP, or L3_DEFAULT.

Internal passthrough Network Load Balancers support the following IPv6 protocol options for each forwarding rule: TCP or UDP.

The L3_DEFAULT option enables you to load balance TCP, UDP, ICMP, ICMPv6, SCTP, ESP, AH, and GRE protocols.

In addition to supporting protocols other than TCP and UDP, the L3_DEFAULT option makes it possible for a single forwarding rule to simultaneously forward traffic for multiple protocols. For example, in addition to making HTTP requests, you can also ping the load balancer IP address.

Forwarding rules that use the TCP or UDP protocols can reference a backend service by using either the same protocol as the forwarding rule or a backend service using UNSPECIFIED protocol.

If you're using the L3_DEFAULT protocol, you must configure the forwarding rule to accept traffic on all ports. To configure all ports, either set --ports=ALL by using the Google Cloud CLI, or set allPorts to True by using the API.

The following table summarizes how to use these settings for different protocols:

Traffic to be load-balanced Forwarding rule protocol Backend service protocol
TCP (IPv4 or IPv6) TCP TCP or UNSPECIFIED
UDP (IPv4 or IPv6) UDP UDP or UNSPECIFIED
TCP, UDP, ICMP, ICMPv6, SCTP, ESP, AH, and GRE L3_DEFAULT UNSPECIFIED

Forwarding rules and global access

An internal passthrough Network Load Balancer's forwarding rules are regional, even when global access is enabled. After you enable global access, the regional internal forwarding rule's allowGlobalAccess flag is set to true.

Forwarding rules and port specifications

When you create an internal forwarding rule, you must choose one of the following port specifications:

  • Specify at least one and up to five ports, by number.
  • Specify ALL to forward traffic on all ports.

An internal forwarding rule that supports either all TCP ports or all UDP ports allows backend VMs to run multiple applications, each on its own port. Traffic sent to a given port is delivered to the corresponding application, and all applications use the same IP address.

When you need to forward traffic on more than five specific ports, combine firewall rules with forwarding rules. When you create the forwarding rule, specify all ports, and then create ingress allow firewall rules that only permit traffic to the desired ports. Apply the firewall rules to the backend VMs.

You cannot modify a forwarding rule after you create it. If you need to change the specified ports or the internal IP address for an internal forwarding rule, you must delete and recreate it.

Multiple forwarding rules for a single backend service

You can configure multiple internal forwarding rules that all reference the same internal backend service. An internal passthrough Network Load Balancer requires at least one internal forwarding rule.

Configuring multiple forwarding rules for the same backend service lets you do the following:

  • Assign multiple IP addresses to the load balancer. You can create multiple forwarding rules, each using a unique IP address. Each forwarding rule can specify all ports or a set of up to five ports.

  • Assign a specific set of ports, using the same IP address, to the load balancer. You can create multiple forwarding rules sharing the same IP address, where each forwarding rule uses a specific set of up to five ports. This is an alternative to configuring a single forwarding rule that specifies all ports.

For more information about scenarios involving two or more internal forwarding rules that share a common internal IP address, see Multiple forwarding rules with the same IP address.

When using multiple internal forwarding rules, make sure that you configure the software running on your backend VMs to bind to all of the forwarding rule IP addresses or to any address (0.0.0.0/0 for IPv4 or ::/0 for IPv6). The destination IP address for a packet delivered through the load balancer is the internal IP address associated with the corresponding internal forwarding rule. For more information, see TCP and UDP request and return packets.

Backend service

Each internal passthrough Network Load Balancer has one regional internal backend service that defines backend parameters and behavior. The name of the backend service is the name of the internal passthrough Network Load Balancer shown in the Google Cloud console.

Each backend service defines the following backend parameters:

  • Protocol. A backend service supports IPv4 and IPv6 traffic. If the protocol has a concept of a port (like TCP or UDP), the backend service delivers packets to backend VMs on the same destination port to which traffic was sent.

    Backend services support the following IPv4 protocol options: TCP, UDP, or UNSPECIFIED.

    Backend services support the following IPv6 protocol options: TCP or UDP. The backend service protocol must coordinate with the forwarding rule protocol.

    For a table with possible forwarding rule and backend service protocol combinations, see Forwarding rule protocol specification.

  • Traffic distribution. A backend service allows traffic to be distributed according to a configurable session affinity.

  • Health check. A backend service must have an associated health check.

Each backend service operates in a single region and distributes traffic for backend VMs in a single VPC network:

Instance group backends and network interfaces

The VPC network associated with an instance group is the VPC network used by every member VM's nic0 network interface.

  • For managed instance groups (MIGs), the VPC network for the instance group is defined in the instance template.
  • For unmanaged instance groups, the VPC network for the instance group is defined as the VPC network used by the nic0 network interface of the first VM instance that you add to the unmanaged instance group.

Within a given (managed or unmanaged) instance group, all VM instances must have their nic0 network interfaces in the same VPC network. Each member VM can optionally have additional network interfaces (nic1 through nic7), but each network interface must attach to a different VPC network. These networks must also be different from the VPC network associated with the instance group.

Zonal NEG backends and network interfaces

When you create a new zonal NEG with GCE_VM_IP endpoints, you must explicitly associate the NEG with a subnetwork of a VPC network before you can add any endpoints to the NEG. Neither the subnet nor the VPC network can be changed after the NEG is created.

Within a given NEG, each GCE_VM_IP endpoint actually represents a network interface. The network interface must be in the subnetwork associated with the NEG. From the perspective of a Compute Engine instance, the network interface can use any identifier (nic0 through nic7). From the perspective of being an endpoint in a NEG, the network interface is identified by using its primary IPv4 address.

There are two ways to add a GCE_VM_IP endpoint to a NEG:

  • If you specify only a VM name (without any IP address) when adding an endpoint, Google Cloud requires that the VM has a network interface in the subnetwork associated with the NEG. The IP address that Google Cloud chooses for the endpoint is the primary internal IPv4 address of the VM's network interface in the subnetwork associated with the NEG.
  • If you specify both a VM name and an IP address when adding an endpoint, the IP address that you provide must be a primary internal IPv4 address for one of the VM's network interfaces. That network interface must be in the subnetwork associated with the NEG. Note that specifying an IP address is redundant because there can only be a single network interface that is in the subnetwork associated with the NEG.

Backend service network specification

You can explicitly associate a VPC network with a backend service by using the --network flag when you create the backend service. The backend service network rules go into effect immediately.

If you omit the --network flag when you create a backend service, Google Cloud uses one of the following qualifying events to implicitly set the backend service's associated VPC network. After it is set, the backend service's associated VPC network cannot be changed:

  • If the backend service doesn't yet have any associated backends, and you configure the first forwarding rule to reference the backend service, Google Cloud sets the backend service's associated VPC network to the VPC network that contains the subnet used by this forwarding rule.

  • If the backend service doesn't yet have a forwarding rule referencing it, and you add the first instance group backend to the backend service, Google Cloud sets the backend service's VPC network to the VPC network associated with that first instance group backend. This means that the backend service's associated VPC network is the network used by the nic0 network interface of each VM in the first instance group backend.

  • If the backend service doesn't yet have a forwarding rule referencing it, and you add the first zonal NEG backend (with GCE_VM_IP endpoints) to the backend service, Google Cloud sets the backend service's VPC network to the VPC network associated with that first NEG backend.

After the backend service's VPC network has been set by a qualifying event, any additional forwarding rules, backend instance groups, or backend zonal NEGs that you add must follow the backend service network rules.

Backend service network rules

The following rules apply after a backend service is associated with a specific VPC network:

  • When configuring a forwarding rule to reference the backend service, the forwarding rule must use a subnet of the backend service's VPC network. The forwarding rule and backend service cannot use different VPC networks, even if those networks are connected by using VPC Network Peering.

  • When adding instance group backends, one of the following must be true:

    • The VPC network associated with the instance group—that is, the VPC network used by the nic0 network interface of each VM in the instance group—must match the backend service's associated VPC network.
    • Each backend VM must have a non-nic0 interface (nic1 through nic7) in the VPC network associated with the backend service.

  • When adding zonal NEG backends with GCE_VM_IP endpoints, the VPC network associated with the NEG must match the VPC network associated with the backend service.

Dual-stack backends (IPv4 and IPv6)

If you want the load balancer to use dual-stack backends that handle both IPv4 and IPv6 traffic, note the following requirements:

  • Backends must be configured in dual-stack subnets that are in the same region as the load balancer's IPv6 forwarding rule. For the backends, you can use a subnet with the ipv6-access-type set to either INTERNAL or EXTERNAL. If the backend subnet's ipv6-access-type is set to EXTERNAL, you must use a different dual-stack or IPv6-only subnet with ipv6-access-type set to INTERNAL for the load balancer's internal forwarding rule. For more information, see Add a dual-stack subnet.
  • Backends must be configured to be dual-stack with stack-type set to IPv4_IPv6. If the backend subnet's ipv6-access-type is set to EXTERNAL, you must also set the --ipv6-network-tier to PREMIUM. For more information, see Create an instance template with IPv6 addresses.

IPv6-only backends

If you want the load balancer to use IPv6-only backends, note the following requirements:

  • IPv6-only instances are only supported in unmanaged instance groups. No other backend type is supported.
  • Backends must be configured in either dual-stack or IPv6-only subnets that are in the same region as the load balancer's IPv6 forwarding rule. For the backends, you can use a subnet with the ipv6-access-type set to either INTERNAL or EXTERNAL. If the backend subnet's ipv6-access-type is set to EXTERNAL, you must use a different IPv6-only subnet with ipv6-access-type set to INTERNAL for the load balancer's internal forwarding rule.
  • Backends must be configured to be IPv6-only with the VM stack-type set to IPv6_ONLY. If the backend subnet's ipv6-access-type is set to EXTERNAL, you must also set the --ipv6-network-tier to PREMIUM. For more information, see Create an instance template with IPv6 addresses.

Note that IPv6-only VMs can be created under both dual-stack and IPv6-only subnets, but dual-stack VMs can't be created under IPv6-only subnets.

Backend subsetting

Backend subsetting is an optional feature that improves performance by limiting the number of backends to which traffic is distributed.

You should only enable subsetting if you need to support more than 250 backend VMs on a single load balancer. For more information, see Backend subsetting for internal passthrough Network Load Balancer.

Health check

The load balancer's backend service must be associated with a global or regional health check. Special routes outside of the VPC network facilitate communication between health check systems and the backends.

You can use an existing health check or define a new one. The internal passthrough Network Load Balancers use health check status to determine how to route new connections, as described in Traffic distribution.

You can use any of the following health check protocols; the protocol of the health check does not have to match the protocol of the load balancer:

  • HTTP, HTTPS, or HTTP/2. If your backend VMs serve traffic by using HTTP, HTTPS, or HTTP/2, it's best to use a health check that matches that protocol because HTTP-based health checks offer options appropriate to that protocol. Serving HTTP-type traffic through an internal passthrough Network Load Balancer means that the load balancer's protocol is TCP.
  • SSL or TCP. If your backend VMs do not serve HTTP-type traffic, you should use either an SSL or TCP health check.

Regardless of the type of health check that you create, Google Cloud sends health check probes to the IP address of the internal passthrough Network Load Balancer's forwarding rule, to the network interface in the VPC network selected by the load balancer's backend service. This simulates how load balanced traffic is delivered. Software running on your backend VMs must respond to both load balanced traffic and health check probes sent to each forwarding rule's IP address (the software must listen on 0.0.0.0:<port> and not on a specific IP address assigned to a network interface). For more information, see Destination for probe packets.

Health checks and UDP traffic

Google Cloud does not offer a health check that uses the UDP protocol. When you use an internal passthrough Network Load Balancer with UDP traffic, you must run a TCP-based service on your backend VMs to provide health check information.

In this configuration, client requests are load balanced by using the UDP protocol, and a TCP service is used to provide information to Google Cloud health check probers. For example, you can run a simple HTTP server on each backend VM that returns an HTTP 200 response to Google Cloud. In this example, you should use your own logic running on the backend VM to ensure that the HTTP server returns 200 only if the UDP service is properly configured and running.

High availability architecture

The internal passthrough Network Load Balancer is highly available by design. There are no special steps to make the load balancer highly available because the mechanism doesn't rely on a single device or VM instance.

To ensure that your backend VM instances are deployed to multiple zones, follow these deployment recommendations:

  • Use regional managed instance groups if you can deploy your software by using instance templates. Regional managed instance groups automatically distribute traffic among multiple zones, providing the best option to avoid potential issues in any given zone.

  • If you use zonal managed instance groups or unmanaged instance groups, use multiple instance groups in different zones (in the same region) for the same backend service. Using multiple zones protects against potential issues in any given zone.

Shared VPC architecture

The following table summarizes the component requirements for internal passthrough Network Load Balancers used with Shared VPC networks. For an example, see creating an internal passthrough Network Load Balancer on the Provisioning Shared VPC page.

IP address Forwarding rule Backend components
An internal IP address must be defined in the same project as the backend VMs.

For the load balancer to be available in a Shared VPC network, the Google Cloud internal IP address must be defined in the same service project where the backend VMs are located, and it must reference a subnet in the desired Shared VPC network in the host project. The address itself comes from the primary IP range of the referenced subnet.

If you create an internal IP address in a service project and the IP address subnet is in the service project's VPC network, your internal passthrough Network Load Balancer is local to the service project. It's not local to any Shared VPC host project.		 An internal forwarding rule must be defined in the same project as the backend VMs.

For the load balancer to be available in a Shared VPC network, the internal forwarding rule must be defined in the same service project where the backend VMs are located, and it must reference the same subnet (in the Shared VPC network) that the associated internal IP address references.

If you create an internal forwarding rule in a service project and the forwarding rule's subnet is in the service project's VPC network, your internal passthrough Network Load Balancer is local to the service project. It's not local to any Shared VPC host project.		 In a Shared VPC scenario, backend VMs are located in a service project. A regional internal backend service and health check must be defined in that service project.

Traffic distribution

Internal passthrough Network Load Balancers support a variety of traffic distribution customization options, including session affinity, connection tracking, and failover. For details about how internal passthrough Network Load Balancers distribute traffic, and how these options interact with each other, see Traffic distribution for internal passthrough Network Load Balancers.

Quotas and limits

For information about quotas and limits, see Load balancing resource quotas.

Limitations

  • You cannot use the Google Cloud console to create an internal passthrough Network Load Balancer with zonal NEG backends.

What's next