grpc/doc/xds-test-descriptions.md

xDS (Load-Balancing) Interop Test Case Descriptions

Client and server use test.proto.

Server

The code for the xDS test server can be found at: Java (other language implementations are in progress).

Server should accept these arguments:

• --port=PORT
  • The port the server will run on.

Client

The base behavior of the xDS test client is to send a constant QPS of unary messages and record the remote-peer distribution of the responses. Further, the client must expose an implementation of the LoadBalancerStatsService gRPC service to allow the test driver to validate the load balancing behavior for a particular test case (see below for more details).

The code for the xDS test client can be at: Java (other language implementations are in progress).

Clients should accept these arguments:

• --fail_on_failed_rpcs=BOOL
  • If true, the client should exit with a non-zero return code if any RPCs fail after at least one RPC has succeeded, indicating a valid xDS config was received. This accounts for any startup-related delays in receiving an initial config from the load balancer. Default is false.
• --num_channels=CHANNELS
  • The number of channels to create to the server.
• --qps=QPS
  • The QPS per channel.
• --server=HOSTNAME:PORT
  • The server host to connect to. For example, "localhost:8080"
• --stats_port=PORT
  • The port for to expose the client's LoadBalancerStatsService implementation.
• --rpc_timeout_sec=SEC
  • The timeout to set on all outbound RPCs. Default is 20.

Test Driver

Note that, unlike our other interop tests, neither the client nor the server has any notion of which of the following test scenarios is under test. Instead, a separate test driver is responsible for configuring the load balancer and the server backends, running the client, and then querying the client's LoadBalancerStatsService to validate load balancer behavior for each of the tests described below.

LoadBalancerStatsService

The service is defined as:

message LoadBalancerStatsRequest {
  // Request stats for the next num_rpcs sent by client.
  int32 num_rpcs = 1;
  // If num_rpcs have not completed within timeout_sec, return partial results.
  int32 timeout_sec = 2;
}

message LoadBalancerStatsResponse {
  // The number of completed RPCs for each peer.
  map<string, int32> rpcs_by_peer = 1;
  // The number of RPCs that failed to record a remote peer.
  int32 num_failures = 2;
}

service LoadBalancerStatsService {
  // Gets the backend distribution for RPCs sent by a test client.
  rpc GetClientStats(LoadBalancerStatsRequest)
      returns (LoadBalancerStatsResponse) {}
}

Note that the LoadBalancerStatsResponse contains the remote peer distribution of the next num_rpcs sent by the client after receiving the LoadBalancerStatsRequest. It is important that the remote peer distribution be recorded for a block of consecutive outgoing RPCs, to validate the intended distribution from the load balancer, rather than just looking at the next num_rpcs responses received from backends, as different backends may respond at different rates.

Test Cases

ping_pong

This test verifies that every backend receives traffic.

Client parameters:

1. --num_channels=1
2. --qps=100
3. --fail_on_failed_rpc=true

Load balancer configuration:

1. 4 backends are created in a single managed instance group (MIG).

Test driver asserts:

1. All backends receive at least one RPC

round_robin

This test verifies that RPCs are evenly routed according to an unweighted round robin policy.

Client parameters:

1. --num_channels=1
2. --qps=100
3. --fail_on_failed_rpc=true

Load balancer configuration:

1. 4 backends are created in a single MIG.

Test driver asserts that:

1. Once all backends receive at least one RPC, the following 100 RPCs are evenly distributed across the 4 backends.

backends_restart

This test verifies that the load balancer will resume sending traffic to a set of backends that is stopped and then resumed.

Client parameters:

1. --num_channels=1
2. --qps=100

Load balancer configuration:

1. 4 backends are created in a single MIG.

Test driver asserts:

1. All backends receive at least one RPC.

The test driver records the peer distribution for a subsequent block of 100 RPCs then stops the backends.

Test driver asserts:

1. No RPCs from the client are successful.

The test driver resumes the backends.

Test driver asserts:

1. Once all backends receive at least one RPC, the distribution for a block of 100 RPCs is the same as the distribution recorded prior to restart.

secondary_locality_gets_requests_on_primary_failure

This test verifies that backends in a secondary locality receive traffic when all backends in the primary locality fail.

Client parameters:

1. --num_channels=1
2. --qps=100

Load balancer configuration:

1. The primary MIG with 2 backends in the same zone as the client
2. The secondary MIG with 2 backends in a different zone

Test driver asserts:

1. All backends in the primary locality receive at least 1 RPC.
2. No backends in the secondary locality receive RPCs.

The test driver stops the backends in the primary locality.

Test driver asserts:

1. All backends in the secondary locality receive at least 1 RPC.

The test driver resumes the backends in the primary locality.

Test driver asserts:

1. All backends in the primary locality receive at least 1 RPC.
2. No backends in the secondary locality receive RPCs.

secondary_locality_gets_no_requests_on_partial_primary_failure

This test verifies that backends in a failover locality do not receive traffic when at least one of the backends in the primary locality remain healthy.

Note: Future TD features may change the expected behavior and require changes to this test case.

Client parameters:

1. --num_channels=1
2. --qps=100

Load balancer configuration:

1. The primary MIG with 2 backends in the same zone as the client
2. The secondary MIG with 2 backends in a different zone

Test driver asserts:

1. All backends in the primary locality receive at least 1 RPC.
2. No backends in the secondary locality receive RPCs.

The test driver stops one of the backends in the primary locality.

Test driver asserts:

1. All backends in the primary locality receive at least 1 RPC.
2. No backends in the secondary locality receive RPCs.

remove_instance_group

This test verifies that a remaining instance group can successfully serve RPCs after removal of another instance group in the same zone.

Client parameters:

1. --num_channels=1
2. --qps=100

Load balancer configuration:

1. Two MIGs with two backends each, using rate balancing mode.

Test driver asserts:

1. All backends receive at least one RPC.

The test driver removes one MIG.

Test driver asserts:

1. All RPCs are directed to the two remaining backends (no RPC failures).

change_backend_service

This test verifies that the backend service can be replaced and traffic routed to the new backends.

Client parameters:

1. --num_channels=1
2. --qps=100
3. --fail_on_failed_rpc=true

Load balancer configuration:

1. One MIG with two backends

Test driver asserts:

1. All backends receive at least one RPC.

The test driver creates a new backend service containing a MIG with two backends and changes the TD URL map to point to this new backend service.

Test driver asserts:

1. All RPCs are directed to the new backend service.

traffic_splitting

This test verifies that the traffic will be distributed between backend services with the correct weights when route action is set to weighted backend services.

Client parameters:

1. --num_channels=1
2. --qps=100

Load balancer configuration:

1. One MIG with one backend

Assert:

1. Once all backends receive at least one RPC, the following 1000 RPCs are all sent to MIG_a.

The test driver adds a new MIG with 1 backend, and changes the route action to weighted backend services with {a: 20, b: 80}.

Assert:

1. Once all backends receive at least one RPC, the following 1000 RPCs are distributed across the 2 backends as a: 20, b: 80.

gentle_failover

This test verifies that traffic is partially diverted to a secondary locality when > 50% of the instances in the primary locality are unhealthy.

Client parameters:

1. --num_channels=1
2. --qps=100

Load balancer configuration:

1. The primary MIG with 3 backends in the same zone as the client
2. The secondary MIG with 2 backends in a different zone

Test driver asserts:

1. All backends in the primary locality receive at least 1 RPC.
2. No backends in the secondary locality receive RPCs.

The test driver stops 2 of 3 backends in the primary locality.

Test driver asserts:

1. All backends in the secondary locality receive at least 1 RPC.
2. The remaining backend in the primary locality receives at least 1 RPC.

The test driver resumes the backends in the primary locality.

Test driver asserts:

1. All backends in the primary locality receive at least 1 RPC.
2. No backends in the secondary locality receive RPCs.