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http_client output

Sends messages to an HTTP server.

# Common config fields, showing default values
output:
  label: ""
  http_client:
    url: "" # No default (required)
    verb: "POST"
    headers: {}
    rate_limit: "" # No default (optional)
    timeout: "5s"
    max_in_flight: 64
    batching:
      count: 0
      byte_size: 0
      period: ""
      check: ""

When the number of retries expires the output will reject the message, the behavior after this will depend on the pipeline but usually this simply means the send is attempted again until successful whilst applying back pressure.

The URL and header values of this type can be dynamically set using function interpolations described in Bloblang queries.

The body of the HTTP request is the raw contents of the message payload. If the message has multiple parts (is a batch) the request will be sent according to RFC1341. This behavior can be disabled by setting the field batch_as_multipart to false.

Propagate responses​

It's possible to propagate the response from each HTTP request back to the input source by setting propagate_response to true. Only inputs that support synchronous responses are able to make use of these propagated responses.

Performance​

This output benefits from sending multiple messages in flight in parallel for improved performance. You can tune the max number of in flight messages (or message batches) with the field max_in_flight.

This output benefits from sending messages as a batch for improved performance. Batches can be formed at both the input and output level. You can find out more in this doc.

Fields​

url​

The URL to connect to.

This field supports interpolation functions.

Type: string

verb​

A verb to connect with

Type: string
Default: "POST"

headers​

A map of headers to add to the request.

This field supports interpolation functions.

Type: map of string
Default: {}

metadata​

Specify optional matching rules to determine which metadata keys should be added to the HTTP request as headers.

Type: object

metadata.include_prefixes​

Provide a list of explicit metadata key prefixes to match against.

Type: array of string
Default: []

metadata.include_patterns​

Provide a list of explicit metadata key regular expression (re2) patterns to match against.

Type: array of string
Default: []

dump_request_log_level​

EXPERIMENTAL: Optionally set a level at which the request and response payload of each request made will be logged.

Type: string
Default: ""

Options: TRACE, DEBUG, INFO, WARN, ERROR, FATAL, ``

oauth​

Allows you to specify open authentication via OAuth version 1.

Type: object

oauth.enabled​

Whether to use OAuth version 1 in requests.

Type: bool
Default: false

oauth.consumer_key​

A value used to identify the client to the service provider.

Type: string
Default: ""

oauth.consumer_secret​

A secret used to establish ownership of the consumer key.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

oauth.access_token​

A value used to gain access to the protected resources on behalf of the user.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

oauth.access_token_secret​

A secret provided in order to establish ownership of a given access token.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

oauth2​

Allows you to specify open authentication via OAuth version 2 using the client credentials token flow.

Type: object

oauth2.enabled​

Whether to use OAuth version 2 in requests.

Type: bool
Default: false

oauth2.client_key​

A value used to identify the client to the token provider.

Type: string
Default: ""

oauth2.client_secret​

A secret used to establish ownership of the client key.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

oauth2.token_url​

The URL of the token provider.

Type: string
Default: ""

oauth2.scopes​

A list of optional requested permissions.

Type: array of string
Default: []

oauth2.endpoint_params​

A list of optional endpoint parameters, values should be arrays of strings.

Type: map of unknown
Default: {}

basic_auth​

Allows you to specify basic authentication.

Type: object

basic_auth.enabled​

Whether to use basic authentication in requests.

Type: bool
Default: false

basic_auth.username​

A username to authenticate as.

Type: string
Default: ""

basic_auth.password​

A password to authenticate with.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

jwt​

BETA: Allows you to specify JWT authentication.

Type: object

jwt.enabled​

Whether to use JWT authentication in requests.

Type: bool
Default: false

jwt.private_key_file​

A file with the PEM encoded via PKCS1 or PKCS8 as private key.

Type: string
Default: ""

jwt.signing_method​

A method used to sign the token such as RS256, RS384, RS512 or EdDSA.

Type: string
Default: ""

jwt.claims​

A value used to identify the claims that issued the JWT.

Type: map of unknown
Default: {}

jwt.headers​

Add optional key/value headers to the JWT.

Type: map of unknown
Default: {}

tls​

Custom TLS settings can be used to override system defaults.

Type: object

tls.enabled​

Whether custom TLS settings are enabled.

Type: bool
Default: false

tls.skip_cert_verify​

Whether to skip server side certificate verification.

Type: bool
Default: false

tls.enable_renegotiation​

Whether to allow the remote server to repeatedly request renegotiation. Enable this option if you're seeing the error message local error: tls: no renegotiation.

Type: bool
Default: false

tls.root_cas​

An optional root certificate authority to use. This is a string, representing a certificate chain from the parent trusted root certificate, to possible intermediate signing certificates, to the host certificate.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

tls.root_cas_file​

An optional path of a root certificate authority file to use. This is a file, often with a .pem extension, containing a certificate chain from the parent trusted root certificate, to possible intermediate signing certificates, to the host certificate.

Type: string
Default: ""

tls.client_certs​

A list of client certificates to use. For each certificate either the fields cert and key, or cert_file and key_file should be specified, but not both.

Type: array of object
Default: []

tls.client_certs[].cert​

A plain text certificate to use.

Type: string
Default: ""

tls.client_certs[].key​

A plain text certificate key to use.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

tls.client_certs[].cert_file​

The path of a certificate to use.

Type: string
Default: ""

tls.client_certs[].key_file​

The path of a certificate key to use.

Type: string
Default: ""

tls.client_certs[].password​

A plain text password for when the private key is password encrypted in PKCS#1 or PKCS#8 format. The obsolete pbeWithMD5AndDES-CBC algorithm is not supported for the PKCS#8 format.

Because the obsolete pbeWithMD5AndDES-CBC algorithm does not authenticate the ciphertext, it is vulnerable to padding oracle attacks that can let an attacker recover the plaintext.

Secret

This field contains sensitive information. Use a secret reference rather than a literal value.

Type: string
Default: ""

extract_headers​

Specify which response headers should be added to resulting synchronous response messages as metadata. Header keys are lowercased before matching, so ensure that your patterns target lowercased versions of the header keys that you expect. This field is not applicable unless propagate_response is set to true.

Type: object

extract_headers.include_prefixes​

Provide a list of explicit metadata key prefixes to match against.

Type: array of string
Default: []

extract_headers.include_patterns​

Provide a list of explicit metadata key regular expression (re2) patterns to match against.

Type: array of string
Default: []

rate_limit​

An optional rate limit to throttle requests by.

Type: string

timeout​

A static timeout to apply to requests.

Type: string
Default: "5s"

retry_period​

The base period to wait between failed requests.

Type: string
Default: "1s"

max_retry_backoff​

The maximum period to wait between failed requests.

Type: string
Default: "300s"

retries​

The maximum number of retry attempts to make.

Type: int
Default: 3

follow_redirects​

Whether or not to transparently follow redirects, i.e. responses with 300-399 status codes. If disabled, the response message will contain the body, status, and headers from the redirect response and the processor will not make a request to the URL set in the Location header of the response.

Type: bool
Default: true

backoff_on​

A list of status codes whereby the request should be considered to have failed and retries should be attempted, but the period between them should be increased gradually.

Type: array of int
Default: [429]

drop_on​

A list of status codes whereby the request should be considered to have failed but retries should not be attempted. This is useful for preventing wasted retries for requests that will never succeed. Note that with these status codes the request is dropped, but message that caused the request will not be dropped.

Type: array of int
Default: []

successful_on​

A list of status codes whereby the attempt should be considered successful, this is useful for dropping requests that return non-2XX codes indicating that the message has been dealt with, such as a 303 See Other or a 409 Conflict. All 2XX codes are considered successful unless they are present within backoff_on or drop_on, regardless of this field.

Type: array of int
Default: []

proxy_url​

An optional HTTP proxy URL.

Type: string

disable_http2​

Whether or not to disable disable HTTP/2

Type: bool
Default: false

batch_as_multipart​

Send message batches as a single request using RFC1341. If disabled messages in batches will be sent as individual requests.

Type: bool
Default: false

propagate_response​

Whether responses from the server should be propagated back to the input.

Type: bool
Default: false

max_in_flight​

The maximum number of parallel message batches to have in flight at any given time.

Type: int
Default: 64

batching​

Allows you to configure a batching policy.

Type: object

batching.count​

A number of messages at which the batch should be flushed. If 0 disables count based batching.

Type: int
Default: 0

batching.byte_size​

An amount of bytes at which the batch should be flushed. If 0 disables size based batching.

Type: int
Default: 0

batching.period​

A period in which an incomplete batch should be flushed regardless of its size.

Type: string
Default: ""

batching.check​

A Bloblang query that should return a boolean value indicating whether a message should end a batch.

Type: string
Default: ""

batching.processors​

A list of processors to apply to a batch as it is flushed. This allows you to aggregate and archive the batch however you see fit. Please note that all resulting messages are flushed as a single batch, therefore splitting the batch into smaller batches using these processors is a no-op.

Type: array of processor

multipart​

EXPERIMENTAL: Create explicit multipart HTTP requests by specifying an array of parts to add to the request, each part specified consists of content headers and a data field that can be populated dynamically. If this field is populated it will override the default request creation behavior.

Type: array of object
Default: []

multipart[].content_type​

The content type of the individual message part.

This field supports interpolation functions.

Type: string
Default: ""

multipart[].content_disposition​

The content disposition of the individual message part.

This field supports interpolation functions.

Type: string
Default: ""

multipart[].body​

The body of the individual message part.

This field supports interpolation functions.

Type: string
Default: ""

When to Use​

Use http_client output when you need to:

  • Send data to REST APIs — Elasticsearch, webhooks, custom services
  • Forward processed events to downstream HTTP endpoints
  • Integrate with SaaS platforms — Slack, PagerDuty, Datadog

Don't use this if:

  • The destination has a native output — use aws_s3, etc.
  • You need bi-directional communication — use websocket
  • You're sending to Kafka — use kafka

Common Patterns​

POST JSON to API​

output:
  http_client:
    url: "https://api.example.com/events"
    verb: POST
    headers:
      Content-Type: application/json
      Authorization: "Bearer ${API_TOKEN}"

Batch Requests​

Reduce API calls by sending one request per batch. Batching alone doesn't do this: each message of a batch is still sent as its own request. The archive processor joins the batch into a single JSON array, which becomes the request body:

output:
  http_client:
    url: "https://api.example.com/bulk"
    verb: POST
    headers:
      Content-Type: application/json
    batching:
      count: 100
      period: 10s
      processors:
        - archive:
            format: json_array

With Retry​

Handle transient failures. Failed requests are retried up to retries times, waiting retry_period between attempts; for status codes listed in backoff_on the wait grows gradually up to max_retry_backoff.

Retries can duplicate side effects: a request that times out after the server accepted it is sent again, and the endpoint sees it twice. Use an idempotent endpoint, or send an idempotency key the server can deduplicate on. That key has to be identical across attempts and distinct for every event, so read it from something the message already carries, or stamp one before the output:

pipeline:
  processors:
    # Stamped once per message, so every retry of that message reuses it.
    - mapping: 'meta idempotency_key = uuid_v4()'

output:
  http_client:
    url: "https://api.example.com/events"
    verb: POST
    headers:
      Idempotency-Key: '${! @idempotency_key }'
    retries: 5
    retry_period: 2s
    max_retry_backoff: 30s
    backoff_on: [429, 503]

When the event already has an identifier, use that instead (${! json("event_id") }, or a broker-supplied key such as ${! @kafka_key }). It deduplicates retries and also collapses re-deliveries of the same event from an at-least-once input, which a freshly minted key cannot.

Hashing the payload (${! content().hash("sha256").encode("hex") }) is only safe where identical bytes always mean the same event. Two distinct events carrying the same payload, such as a sensor reporting the same reading twice, would share a key and the second would be discarded as a duplicate.