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environment_variables.md

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gRPC environment variables

gRPC C core based implementations (those contained in this repository) expose some configuration as environment variables that can be set.

  • http_proxy The URI of the proxy to use for HTTP CONNECT support.

  • GRPC_ABORT_ON_LEAKS A debugging aid to cause a call to abort() when gRPC objects are leaked past grpc_shutdown(). Set to 1 to cause the abort, if unset or 0 it does not abort the process.

  • GOOGLE_APPLICATION_CREDENTIALS The path to find the credentials to use when Google credentials are created

  • GRPC_SSL_CIPHER_SUITES A colon separated list of cipher suites to use with OpenSSL Defaults to: ECDHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384

  • GRPC_DEFAULT_SSL_ROOTS_FILE_PATH PEM file to load SSL roots from

  • GRPC_POLL_STRATEGY [posix-style environments only] Declares which polling engines to try when starting gRPC. This is a comma-separated list of engines, which are tried in priority order first -> last. Available polling engines include:

    • epoll (linux-only) - a polling engine based around the epoll family of system calls
    • poll - a portable polling engine based around poll(), intended to be a fallback engine when nothing better exists
    • legacy - the (deprecated) original polling engine for gRPC

  • GRPC_TRACE A comma separated list of tracers that provide additional insight into how gRPC C core is processing requests via debug logs. Available tracers include:

    • api - traces api calls to the C core
    • bdp_estimator - traces behavior of bdp estimation logic
    • call_combiner - traces call combiner state
    • call_error - traces the possible errors contributing to final call status
    • channel - traces operations on the C core channel stack
    • client_channel - traces client channel activity, including resolver and load balancing policy interaction
    • compression - traces compression operations
    • connectivity_state - traces connectivity state changes to channels
    • executor - traces grpc's internal thread pool ('the executor')
    • fd_trace - traces fd create(), shutdown() and close() calls for channel fds. Also traces epoll fd create()/close() calls in epollex polling engine traces epoll-fd creation/close calls for epollex polling engine
    • glb - traces the grpclb load balancer
    • handshaker - traces handshaking state
    • health_check_client - traces health checking client code
    • http - traces state in the http2 transport engine
    • http2_stream_state - traces all http2 stream state mutations.
    • http1 - traces HTTP/1.x operations performed by gRPC
    • inproc - traces the in-process transport
    • flowctl - traces http2 flow control
    • op_failure - traces error information when failure is pushed onto a completion queue
    • pick_first - traces the pick first load balancing policy
    • plugin_credentials - traces plugin credentials
    • pollable_refcount - traces reference counting of 'pollable' objects (only in DEBUG)
    • resource_quota - trace resource quota objects internals
    • round_robin - traces the round_robin load balancing policy
    • queue_pluck
    • server_channel - lightweight trace of significant server channel events
    • secure_endpoint - traces bytes flowing through encrypted channels
    • timer - timers (alarms) in the grpc internals
    • timer_check - more detailed trace of timer logic in grpc internals
    • transport_security - traces metadata about secure channel establishment
    • tcp - traces bytes in and out of a channel
    • tsi - traces tsi transport security

    The following tracers will only run in binaries built in DEBUG mode. This is accomplished by invoking CONFIG=dbg make <target>

    • alarm_refcount - refcounting traces for grpc_alarm structure
    • metadata - tracks creation and mutation of metadata
    • combiner - traces combiner lock state
    • closure - tracks closure creation, scheduling, and completion
    • pending_tags - traces still-in-progress tags on completion queues
    • polling - traces the selected polling engine
    • polling_api - traces the api calls to polling engine
    • queue_refcount
    • error_refcount
    • stream_refcount
    • workqueue_refcount
    • fd_refcount
    • cq_refcount
    • auth_context_refcount
    • security_connector_refcount
    • resolver_refcount
    • lb_policy_refcount
    • chttp2_refcount

    'all' can additionally be used to turn all traces on. Individual traces can be disabled by prefixing them with '-'.

    'refcount' will turn on all of the tracers for refcount debugging.

    if 'list_tracers' is present, then all of the available tracers will be printed when the program starts up.

    Example: export GRPC_TRACE=all,-pending_tags

  • GRPC_VERBOSITY Default gRPC logging verbosity - one of:

    • DEBUG - log all gRPC messages
    • INFO - log INFO and ERROR message
    • ERROR - log only errors

  • GRPC_TRACE_FUZZER if set, the fuzzers will output trace (it is usually supressed).

  • GRPC_DNS_RESOLVER Declares which DNS resolver to use. The default is ares if gRPC is built with c-ares support. Otherwise, the value of this environment variable is ignored. Available DNS resolver include:

    • native (default)- a DNS resolver based around getaddrinfo(), creates a new thread to perform name resolution
    • ares - a DNS resolver based around the c-ares library

  • GRPC_CLIENT_CHANNEL_BACKUP_POLL_INTERVAL_MS Default: 5000 Declares the interval between two backup polls on client channels. These polls are run in the timer thread so that gRPC can process connection failures while there is no active polling thread. They help reconnect disconnected client channels (mostly due to idleness), so that the next RPC on this channel won't fail. Set to 0 to turn off the backup polls.

  • GRPC_EXPERIMENTAL_DISABLE_FLOW_CONTROL if set, flow control will be effectively disabled. Max out all values and assume the remote peer does the same. Thus we can ignore any flow control bookkeeping, error checking, and decision making

  • grpc_cfstream set to 1 to turn on CFStream experiment. With this experiment gRPC uses CFStream API to make TCP connections. The option is only available on iOS platform and when macro GRPC_CFSTREAM is defined.