A number of environment variables can be used to configure the behavior of the library. There are also functions to configure this behavior in code. The environment variables are convenient when troubleshooting problems.

Endpoint Overrides

GOOGLE_CLOUD_CPP_IAM_CREDENTIALS_ENDPOINT=... overrides the EndpointOption (which defaults to "iamcredentials.googleapis.com") used by MakeIAMCredentialsConnection().
GOOGLE_CLOUD_CPP_IAM_ENDPOINT=... overrides the EndpointOption (which defaults to "iam.googleapis.com") used by MakeIAMConnection().
GOOGLE_CLOUD_CPP_IAM_POLICY_ENDPOINT=... overrides the EndpointOption (which defaults to "iam-meta-api.googleapis.com") used by MakeIAMPolicyConnection().
GOOGLE_CLOUD_CPP_POLICIES_ENDPOINT=... overrides the EndpointOption (which defaults to "iam.googleapis.com") used by MakePoliciesConnection().

See also: google::cloud::EndpointOption

Logging

GOOGLE_CLOUD_CPP_ENABLE_TRACING=rpc: turns on tracing for most gRPC calls. The library injects an additional Stub decorator that prints each gRPC request and response. Unless you have configured your own logging backend, you should also set GOOGLE_CLOUD_CPP_ENABLE_CLOG to produce any output on the program's console.

See also: google::cloud::TracingComponentsOption

GOOGLE_CLOUD_CPP_TRACING_OPTIONS=...: modifies the behavior of gRPC tracing, including whether messages will be output on multiple lines, or whether string/bytes fields will be truncated.

See also: google::cloud::GrpcTracingOptionsOption

GOOGLE_CLOUD_CPP_ENABLE_CLOG=yes: turns on logging in the library, basically the library always "logs" but the logging infrastructure has no backend to actually print anything until the application sets a backend or they set this environment variable.

See also: google::cloud::LogBackend; google::cloud::LogSink

Setting the Default Project

GOOGLE_CLOUD_PROJECT=...: is used in examples and integration tests to configure the GCP project. This has no effect in the library.