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Open source

loki.write

loki.write receives log entries from other loki components and sends them over the network using Loki’s logproto format.

Multiple loki.write components can be specified by giving them different labels.

Usage

Alloy 
loki.write "LABEL" {
  endpoint {
    url = REMOTE_WRITE_URL
  }
}

Arguments

loki.write supports the following arguments:

NameTypeDescriptionDefaultRequired
max_streamsintTime to wait before marking a request as failed."5s"no
external_labelsmap(string)Labels to add to logs sent over the network.no

Blocks

The following blocks are supported inside the definition of loki.write:

HierarchyBlockDescriptionRequired
endpointendpointLocation to send logs to.no
endpoint > http_client_confighttp_client_configHTTP client settings when connecting to the endpoint.no
endpoint > http_client_config > basic_authbasic_authConfigure basic_auth for authenticating to the endpoint.no
endpoint > http_client_config > authorizationauthorizationConfigure generic authorization to the endpoint.no
endpoint > http_client_config > oauth2oauth2Configure OAuth2 for authenticating to the endpoint.no
endpoint > http_client_config > oauth2 > tls_configtls_configConfigure TLS settings for connecting to the endpoint.no
endpoint > http_client_config > tls_configtls_configConfigure TLS settings for connecting to the endpoint.no

The > symbol indicates deeper levels of nesting. For example, endpoint > http_client_config refers to an http_client_config block defined inside an endpoint block.

endpoint block

The endpoint block describes a single location to send logs to. Multiple endpoint blocks can be provided to send logs to multiple locations.

The following arguments are supported:

NameTypeDescriptionDefaultRequired
urlstringFull URL to send logs to.yes
namestringOptional name to identify this endpoint with.no
batch_waitboolMaximum amount of time to wait before sending a batch."1s"no
batch_sizestringMaximum batch size of logs to accumulate before sending."1MiB"no
remote_timeoutdurationTimeout for requests made to the URL."10s"no
tenant_idstringThe tenant ID used by default to push logs.no
min_backoff_perioddurationInitial backoff time between retries."500ms"no
max_backoff_perioddurationMaximum backoff time between retries."5m"no
max_backoff_retriesintMaximum number of retries.10no

If no tenant_id is provided, the component assumes that the Loki instance at endpoint is running in single-tenant mode and no X-Scope-OrgID header is sent.

When multiple endpoint blocks are provided, the loki.write component creates a client for each. Received log entries are fanned-out to these clients in succession. That means that if one client is bottlenecked, it may impact the rest.

Endpoints can be named for easier identification in debug metrics by using the name argument. If the name argument isn’t provided, a name is generated based on a hash of the endpoint settings.

http_client_config block

The http_client_config configures settings used to connect to the Loki API.

NameTypeDescriptionDefaultRequired
bearer_tokensecretBearer token to authenticate with.no
bearer_token_filestringFile containing a bearer token to authenticate with.no
proxy_urlstringHTTP proxy to proxy requests through.no
follow_redirectsboolWhether redirects returned by the server should be followed.trueno
enable_http_2boolWhether HTTP2 is supported for requests.trueno

bearer_token, bearer_token_file, basic_auth, authorization, and oauth2 are mutually exclusive and only one can be provided inside of a http_client_config block.

basic_auth block

NameTypeDescriptionDefaultRequired
usernamestringBasic auth username.no
passwordsecretBasic auth password.no
password_filestringFile containing the basic auth password.no

password and password_file are mututally exclusive and only one can be provided inside of a basic_auth block.

authorization block

NameTypeDescriptionDefaultRequired
typestringAuthorization type, for example, “Bearer”.no
credentialsecretSecret value.no
credentials_filestringFile containing the secret value.no

credential and credentials_file are mutually exclusive and only one can be provided inside of an authorization block.

oauth2 block

NameTypeDescriptionDefaultRequired
client_idstringOAuth2 client ID.no
client_secretsecretOAuth2 client secret.no
client_secret_filestringFile containing the OAuth2 client secret.no
scopeslist(string)List of scopes to authenticate with.no
token_urlstringURL to fetch the token from.no
endpoint_paramsmap(string)Optional parameters to append to the token URL.no
proxy_urlstringOptional proxy URL for OAuth2 requests.no

client_secret and client_secret_file are mututally exclusive and only one can be provided inside of an oauth2 block.

The oauth2 block may also contain its own separate tls_config sub-block.

tls_config block

NameTypeDescriptionDefaultRequired
ca_filestringCA certificate to validate the server with.no
cert_filestringCertificate file for client authentication.no
key_filestringKey file for client authentication.no
server_namestringServerName extension to indicate the name of the server.no
insecure_skip_verifyboolDisables validation of the server certificate.no
min_versionstringMinimum acceptable TLS version.no

When min_version is not provided, the minimum acceptable TLS version is inherited from Go’s default minimum version, TLS 1.2. If min_version is provided, it must be set to one of the following strings:

  • "TLS10" (TLS 1.0)
  • "TLS11" (TLS 1.1)
  • "TLS12" (TLS 1.2)
  • "TLS13" (TLS 1.3)

Exported fields

The following fields are exported and can be referenced by other components:

NameTypeDescription
receiverLogsReceiverA value that other components can use to send log entries to.

Component health

loki.write is only reported as unhealthy if given an invalid configuration.

Debug information

loki.write does not expose any component-specific debug information.

Debug metrics

  • loki_write_encoded_bytes_total (counter): Number of bytes encoded and ready to send.
  • loki_write_sent_bytes_total (counter): Number of bytes sent.
  • loki_write_dropped_bytes_total (counter): Number of bytes dropped because failed to be sent to the ingester after all retries.
  • loki_write_sent_entries_total (counter): Number of log entries sent to the ingester.
  • loki_write_dropped_entries_total (counter): Number of log entries dropped because they failed to be sent to the ingester after all retries.
  • loki_write_request_duration_seconds (histogram): Duration of sent requests.
  • loki_write_batch_retries_total (counter): Number of times batches have had to be retried.
  • loki_write_stream_lag_seconds (gauge): Difference between current time and last batch timestamp for successful sends.

Example

This example creates a loki.write component that sends received entries to a local Loki instance:

Alloy 
loki.write "local" {
    endpoint {
        url = "loki:3100"
    }
}