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Yandex Application Load Balancer log reference

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Updated at May 19, 2025

This section describes L7 load balancer log fields.

The load balancer provides logs in JSON format. Each log entry corresponds to one client request processed by the load balancer.

For more information, see Logging.

Field Description
type Request type. The possible values are:
  • http: HTTP/1.0 or HTTP/1.1 without encryption.
  • https: HTTP/1.0 or HTTP/1.1 with TLS encryption, i.e., HTTPS or HTTP over TLS.
  • h2: HTTP/2.
  • h3: HTTP/3.
  • grpc: gRPC without encryption.
  • grpcs: gRPC with TLS encryption.
time Date and time when the load balancer received the first byte of the client request in ISO 8601 format, i.e., <YYYY>-<MM>-<DD>T<hh>:<mm>:<ss>Z, where Z is the universal coordinated time (UTC).
http_method HTTP request method.
authority For HTTP/1.0 and HTTP/1.1: Host header value. For other supported protocols: :authority pseudo-header value.
request_uri Request path. For example, /api/v1/foo.
http_status HTTP status code
http_version HTTP version, e.g., HTTP/2
rewritten_request_uri Request path after HTTP router's route substitution, e.g., /api/backend/v1/foo
request_content_type HTTP request Content-Type header value
request_id HTTP request X-Request-ID header value
user_agent HTTP request User-Agent header value identifying the client’s software
referer HTTP request Referer header value identifying the URL from which the request originates
response_content_type Load balancer HTTP response Content-Type header value
client_ip Client IP address
client_port The source TCP port of the client-side connection to the load balancer
backend_ip Internal backend endpoint, e.g., a target group VM or Object Storage bucket, IP address
backend_port Backend port used by the load balancer for establishing connections
load_balancer_id Load balancer ID
http_router_id HTTP router ID
virtual_host_name Virtual host name
route_name Route name
backend_group_id Backend group ID
backend_name Backend name
request_headers_bytes Request header total size in bytes
request_body_bytes Request body size in bytes
response_headers_bytes Response header total size in bytes
response_body_bytes Response body size in bytes
error_details Load balancer error during request processing. The possible values are:
  • no_healthy_backend: No healthy backends. For more information, see Health checks.
  • backend_request_timeout: Backend request timeout specified in the route settings was triggered.
  • balancer_reset: Connection between client and load balancer was reset.
  • backend_connection_closed_before_data_sent_to_client: Load balancer backend connection was reset.
  • failed_to_connect_to_backend: Load balancer failed to connect to the backend.
  • backend_connection_terminated: Backend terminated the connection with the load balancer.
  • no_route: Client's request matches no configured routes in load balancer HTTP routers.
  • client_disconnected: Client terminated the connection with the load balancer.
  • backend_stream_idle_timeout: No data transmitted over the load balancer backend connection for longer than the route’s configured inactivity timeout period.
  • backend_retry_limit_exceeded: Load balancer exceeded maximum backend connection attempts.
  • client_protocol_error: Client protocol error.
tls_version TLS version, e.g., TLSv1.3
cipher_suite TLS encryption ciphers for load balancer client connections
sni_hostname SNI (Server Name Indication) domain name sent to the load balancer by the client during the TLS handshake
server_certificate_subject Domain name specified in the Subject field of the TLS certificate presented by the load balancer to the client
grpc gRPC request information. This field appears in the response for gRPC requests, e.g., "type": "grpc" or "type": "grpcs", only.
  method gRPC request method
  service gRPC service name
  status gRPC request status
   code gRPC error code. For more information on gRPC to HTTP status code mapping, see the google.rpc.Code article.
   message gRPC error description
upstream_transport_failure_reason Message describing the transport layer error that occured during the load balancer backend connection, e.g., TLS connection
request_processing_times Request processing times. All values are specified in seconds.
  request_time Total request time
  response_start_time Latency between the load balancer receiving the first request byte from the client and sending the first response byte back
  request_processing_time Latency between the load balancer receiving the first request byte from the client and sending the first byte to the backend
  backend_processing_time Latency between the load balancer sending the first byte to the backend and receiving the first response byte
  response_processing_time Latency between the load balancer receiving the first byte from the backend and sending the first byte to the client
  request_rx_time Latency between the load balancer receiving the first and last bytes of the client’s request
  request_tx_time Latency between the backend receiving the first and last bytes of the load balancer’s request
  backend_response_time Latency between the load balancer sending the last request byte to the backend and receiving the first response byte
  response_rx_time Latency between the load balancer receiving the first and last bytes of the backend response
  response_tx_time Latency between the load balancer sending the first and last bytes of the response
x_forwarded_for X-Forwarded-For (XFF) request header containing the originating client_ip followed by all intermediate proxy/LB IP addresses the request traversed. For example:
  • x_forwarded_for: 50.0.0.1 shows that the request came from the client directly, with its client_ip added to the header by Application Load Balancer.
  • Conversely, x_forwarded_for: 50.0.0.1,40.0.0.1 shows that the request passed through a proxy server, with its IP address added after client_ip by Application Load Balancer.
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