Documentation Grafana Cloud Instrument and send data Grafana Alloy Reference Components loki loki.write

loki.write

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

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

Usage

alloy Copy

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

Arguments

loki.write supports the following arguments:

Blocks

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

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

endpoint block

The endpoint block describes a single location to send logs to. You can use multiple endpoint blocks to send logs to multiple locations.

The following arguments are supported:

At most, one of the following can be provided:

• bearer_token argument.
• bearer_token_file argument.
• basic_auth block.
• authorization block.
• oauth2 block.

no_proxy can contain IPs, CIDR notations, and domain names. IP and domain names can contain port numbers. proxy_url must be configured if no_proxy is configured.

proxy_from_environment uses the environment variables HTTP_PROXY, HTTPS_PROXY, and NO_PROXY (or the lowercase versions thereof). Requests use the proxy from the environment variable matching their scheme, unless excluded by NO_PROXY. proxy_url and no_proxy must not be configured if proxy_from_environment is configured.

proxy_connect_header should only be configured if proxy_url or proxy_from_environment are configured.

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.

The retry_on_http_429 argument specifies whether HTTP 429 status code responses should be treated as recoverable errors; other HTTP 4xx status code responses are never considered recoverable errors. When retry_on_http_429 is enabled, the retry mechanism will be governed by the backoff configuration specified through min_backoff_period, max_backoff_period and max_backoff_retries attributes.

basic_auth block

password and password_file are mutually exclusive, and only one can be provided inside a basic_auth block.

authorization block

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

oauth2 block

client_secret and client_secret_file are mutually exclusive, and only one can be provided inside an oauth2 block.

The oauth2 block may also contain a separate tls_config sub-block.

no_proxy can contain IPs, CIDR notations, and domain names. IP and domain names can contain port numbers. proxy_url must be configured if no_proxy is configured.

proxy_from_environment uses the environment variables HTTP_PROXY, HTTPS_PROXY, and NO_PROXY (or the lowercase versions thereof). Requests use the proxy from the environment variable matching their scheme, unless excluded by NO_PROXY. proxy_url and no_proxy must not be configured if proxy_from_environment is configured.

proxy_connect_header should only be configured if proxy_url or proxy_from_environment are configured.

tls_config block

The following pairs of arguments are mutually exclusive and can’t both be set simultaneously:

• ca_pem and ca_file
• cert_pem and cert_file
• key_pem and key_file

When configuring client authentication, both the client certificate (using cert_pem or cert_file) and the client key (using key_pem or key_file) must be provided.

When min_version isn’t 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)

queue_config block (experimental)

The optional queue_config block configures, when WAL is enabled, how the underlying client queues batches of logs sent to Loki. Refer to Write-Ahead block for more information.

The following arguments are supported:

wal block (experimental)

The optional wal block configures the Write-Ahead Log (WAL) used in the Loki remote-write client. To enable the WAL, you must include the wal block in your configuration. When the WAL is enabled, the log entries sent to the loki.write component are first written to a WAL under the dir directory and then read into the remote-write client. This process provides durability guarantees when an entry reaches this component. The client knows when to read from the WAL using the following two mechanisms:

• The WAL-writer side of the loki.write component notifies the reader side that new data is available.
• The WAL-reader side periodically checks if there is new data, increasing the wait time exponentially between min_read_frequency and max_read_frequency.

The WAL is located inside a component-specific directory relative to the storage path Alloy is configured to use. See the alloy run documentation for how to change the storage path.

The following arguments are supported:

Exported fields

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

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.

Examples

The following examples show you how to create loki.write components that send log entries to different destinations.

Send log entries to a local Loki instance

You can create a loki.write component that sends your log entries to a local Loki instance:

alloy Copy

loki.write "local" {
    endpoint {
        url = "http://loki:3100/loki/api/v1/push"
    }
}

Send log entries to a managed service

You can create a loki.write component that sends your log entries to a managed service, for example, Grafana Cloud. The Loki username and Grafana Cloud API Key are injected in this example through environment variables.

alloy Copy

loki.write "default" {
    endpoint {
        url = "https://logs-xxx.grafana.net/loki/api/v1/push"
        basic_auth {
            username = sys.env("LOKI_USERNAME")
            password = sys.env("GRAFANA_CLOUD_API_KEY")
        }
    }
}

Technical details

loki.write uses snappy for compression.

Any labels that start with __ will be removed before sending to the endpoint.

Compatible components

loki.write has exports that can be consumed by the following components:

• Components that consume Loki LogsReceiver