loki.write
General availability (GA)

loki.write

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

You can specify multiple loki.write components by giving them different labels.

Usage

alloy
loki.write "<LABEL>" {
  endpoint {
    url = "<REMOTE_WRITE_URL>"
  }
}

Arguments

You can use the following arguments with loki.write:

NameTypeDescriptionDefaultRequired
external_labelsmap(string)Labels to add to logs sent over the network.no
max_streamsintMaximum number of active streams.0 (no limit)no

Blocks

You can use the following blocks with loki.write:

BlockDescriptionRequired
endpointLocation to send logs to.no
endpoint > authorizationConfigure generic authorization to the endpoint.no
endpoint > basic_authConfigure basic_auth for authenticating to the endpoint.no
endpoint > oauth2Configure OAuth 2.0 for authenticating to the endpoint.no
endpoint > oauth2 > tls_configConfigure TLS settings for connecting to the endpoint.no
endpoint > queue_configWhen WAL is enabled, configures the queue client.no
endpoint > tls_configConfigure TLS settings for connecting to the endpoint.no
walWrite-ahead log configuration.no

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

endpoint

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:

NameTypeDescriptionDefaultRequired
urlstringFull URL to send logs to.yes
batch_sizestringMaximum batch size of logs to accumulate before sending."1MiB"no
batch_waitdurationMaximum amount of time to wait before sending a batch."1s"no
bearer_token_filestringFile containing a bearer token to authenticate with.no
bearer_tokensecretBearer token to authenticate with.no
enable_http2boolWhether HTTP2 is supported for requests.trueno
follow_redirectsboolWhether redirects returned by the server should be followed.trueno
headersmap(string)Extra headers to deliver with the request.no
max_backoff_perioddurationMaximum backoff time between retries."5m"no
max_backoff_retriesintMaximum number of retries.10no
min_backoff_perioddurationInitial backoff time between retries."500ms"no
namestringOptional name to identify this endpoint with.no
no_proxystringComma-separated list of IP addresses, CIDR notations, and domain names to exclude from proxying.no
proxy_connect_headermap(list(secret))Specifies headers to send to proxies during CONNECT requests.no
proxy_from_environmentboolUse the proxy URL indicated by environment variables.falseno
proxy_urlstringHTTP proxy to send requests through.no
remote_timeoutdurationTimeout for requests made to the URL."10s"no
retry_on_http_429boolRetry when an HTTP 429 status code is received.trueno
tenant_idstringThe tenant ID used by default to push logs.no

At most, one of the following can be provided:

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 is governed by the backoff configuration specified through min_backoff_period, max_backoff_period and max_backoff_retries attributes.

authorization

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

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

basic_auth

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

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

oauth2

NameTypeDescriptionDefaultRequired
client_idstringOAuth2 client ID.no
client_secret_filestringFile containing the OAuth2 client secret.no
client_secretsecretOAuth2 client secret.no
endpoint_paramsmap(string)Optional parameters to append to the token URL.no
proxy_urlstringHTTP proxy to send requests through.no
no_proxystringComma-separated list of IP addresses, CIDR notations, and domain names to exclude from proxying.no
proxy_from_environmentboolUse the proxy URL indicated by environment variables.falseno
proxy_connect_headermap(list(secret))Specifies headers to send to proxies during CONNECT requests.no
scopeslist(string)List of scopes to authenticate with.no
token_urlstringURL to fetch the token from.no

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.

queue_config

EXPERIMENTAL: This is an experimental feature. Experimental features are subject to frequent breaking changes, and may be removed with no equivalent replacement. The stability.level flag must be set to experimental to use the feature.

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:

NameTypeDescriptionDefaultRequired
capacitystringControls the size of the underlying send queue buffer. This setting should be considered a worst-case scenario of memory consumption, in which all enqueued batches are full.10MiBno
drain_timeoutdurationConfigures the maximum time the client can take to drain the send queue upon shutdown. During that time, it enqueues pending batches and drains the send queue sending each."1m"no

tls_config

NameTypeDescriptionDefaultRequired
ca_pemstringCA PEM-encoded text to validate the server with.no
ca_filestringCA certificate to validate the server with.no
cert_pemstringCertificate PEM-encoded text for client authentication.no
cert_filestringCertificate file for client authentication.no
insecure_skip_verifyboolDisables validation of the server certificate.no
key_filestringKey file for client authentication.no
key_pemsecretKey PEM-encoded text for client authentication.no
min_versionstringMinimum acceptable TLS version.no
server_namestringServerName extension to indicate the name of the server.no

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)

wal

EXPERIMENTAL: This is an experimental feature. Experimental features are subject to frequent breaking changes, and may be removed with no equivalent replacement. The stability.level flag must be set to experimental to use the feature.

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. Refer to the run documentation for more information about how to change the storage path.

The following arguments are supported:

NameTypeDescriptionDefaultRequired
drain_timeoutdurationMaximum time the WAL drain procedure can take, before being forcefully stopped."30s"no
enabledboolWhether to enable the WAL.falseno
max_read_frequencydurationMaximum backoff time in the backup read mechanism."1s"no
max_segment_agedurationMaximum time a WAL segment should be allowed to live. Segments older than this setting are eventually deleted."1h"no
min_read_frequencydurationMinimum backoff time in the backup read mechanism."250ms"no

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 doesn’t expose any component-specific debug information.

Debug metrics

  • loki_write_batch_retries_total (counter): Number of times batches have had to be retried.
  • loki_write_dropped_bytes_total (counter): Number of bytes dropped because failed to be sent to the ingester after all retries.
  • 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_encoded_bytes_total (counter): Number of bytes encoded and ready to send.
  • loki_write_request_duration_seconds (histogram): Duration of sent requests.
  • loki_write_sent_bytes_total (counter): Number of bytes sent.
  • loki_write_sent_entries_total (counter): Number of log entries sent to the ingester.
  • 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
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
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 __ are removed before sending to the endpoint.

Compatible components

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

Note

Connecting some components may not be sensible or components may require further configuration to make the connection work correctly. Refer to the linked documentation for more details.