Splunk HEC
Cribl Stream supports receiving data over HTTP/S using the Splunk HEC (HTTP Event Collector).
Type: Push | TLS Support: YES | Event Breaker Support: YES
This Source supports gzip-compressed inbound data when the
Content‑Encoding: gzipconnection header is set.
Configuring Cribl Stream to Receive Data over Splunk HEC
From the top nav, click Manage, then select a Worker Group to configure. Next, you have two options:
To configure via the graphical QuickConnect UI, click Routing > QuickConnect (Stream) or Collect (Edge). Next, click Add Source at left. From the resulting drawer’s tiles, select [Push > ] Splunk > HEC. Next, click either Add Destination or (if displayed) Select Existing. The resulting drawer will provide the options below.
Or, to configure via the Routing UI, click Data > Sources (Stream) or More > Sources (Edge). From the resulting page’s tiles or left nav, select [Push > ] Splunk > HEC. Next, click New Source to open a New Source modal that provides the options below.
Cribl Stream ships with a Splunk HEC Source preconfigured to listen on Port 8088. You can clone or directly modify this Source to further configure it, and then enable it.
General Settings
Input ID: Enter a unique name to identify this Splunk HEC Source definition. If you clone this Source, Cribl Stream will add -CLONE to the original Input ID.
Address: Enter the hostname/IP on which to listen for HTTP(S) data. Such as: localhost or 0.0.0.0. Supports IPv4 and IPv6 addresses.
Port: Enter the port number.
Splunk HEC endpoint: Absolute path on which to listen for the Splunk HTTP Event Collector API requests. Defaults to /services/collector.
This single endpoint supports JSON events via
/event, health checks via/health, raw events via/raw, and Splunk S2S events via/s2s. See the Splunk REST API endpoints documentation and the examples below. The Source will automatically detect where to forward the request.
Optional Settings
Allowed Indexes: List the values allowed in the HEC event index field. Allows wildcards. Leave blank to skip validation.
Splunk HEC acks: Whether to enable Splunk HEC acknowledgments. Defaults to No. See Working with HEC Acks below to learn about context and limitations.
Tags: Optionally, add tags that you can use to filter and group Sources in Cribl Stream’s Manage Sources page. These tags aren’t added to processed events. Use a tab or hard return between (arbitrary) tag names.
Working with HEC Acks
Cribl Stream sends a 200 or similar HTTP response code when it receives an event.
Some senders also send ack requests, which differ from events. This type of request asks Cribl Stream to acknowledge delivery of an array of event IDs. (A sender might require HEC acks to be enabled. Cribl does not maintain a comprehensive list of senders that require acks – please refer to your sender’s documentation.)
How Cribl Stream responds depends on Optional Settings > Splunk HEC acks:
- When Splunk HEC acks is turned on, Cribl Stream will respond to an ack request with an acknowledgement affirming that Cribl Stream received each of the events whose IDs were listed in the array.
- When Splunk HEC acks is turned off, Cribl Stream will respond to an ack request with a
400error and text saying thatACKis disabled.
It makes sense to turn Splunk HEC acks on for senders that keep TCP connections open while waiting for an ack, because this behavior can exhaust available file descriptors.
There is a caveat to how HEC acks work in Cribl Stream: The ack response simply cites whatever event IDs appeared in the ack request, regardless of whether or not those events were ever received or processed by Cribl Stream. In that sense, what Cribl Stream sends is a “fake ack:” unlike acknowledgements in some other systems, the ack in itself is meaningless. It mainly serves to spare a sender from keeping TCP connections open needlessly.
To determine whether Cribl Stream successfully ingested an event, pay no attention to acks. Instead, verify that the sender received a 200 or similar HTTP response from the Splunk HEC source.
TLS Settings (Server Side)
Enabled defaults to No. When toggled to Yes:
Certificate name: Name of the predefined certificate.
Private key path: Server path containing the private key (in PEM format) to use. Path can reference $ENV_VARS.
Passphrase: Passphrase to use to decrypt private key.
Certificate path: Server path containing certificates (in PEM format) to use. Path can reference $ENV_VARS.
CA certificate path: Server path containing CA certificates (in PEM format) to use. Path can reference $ENV_VARS.
Authenticate client (mutual auth): Require clients to present their certificates. Used to perform mutual authentication using SSL certs. Defaults to No. When toggled to Yes:
Validate client certs: Reject certificates that are not authorized by a CA in the CA certificate path, or by another trusted CA (such as, the system’s CA). Defaults to
No.Common Name: Regex that a peer certificate’s subject attribute must match in order to connect. Defaults to
.*. Matches on the substring afterCN=. As needed, escape regex tokens to match literal characters. (For example, to match the subjectCN=worker.cribl.local, you would enter:worker\.cribl\.local.) If the subject attribute contains Subject Alternative Name (SAN) entries, the Source will check the regex against all of those but ignore the Common Name (CN) entry (if any). If the certificate has no SAN extension, the Source will check the regex against the single name in the CN.
Minimum TLS version: Optionally, select the minimum TLS version to accept from connections.
Maximum TLS version: Optionally, select the maximum TLS version to accept from connections.
Persistent Queue Settings
In this section, you can optionally specify persistent queue storage, using the following controls. This will buffer and preserve incoming events when a downstream Destination is down, or exhibiting backpressure.
On Cribl-managed Cribl.Cloud Workers (with an Enterprise plan), this tab exposes only the Enable Persistent Queue toggle. If enabled, PQ is automatically configured in
Always Onmode, with a maximum queue size of 1 GB disk space allocated per PQ‑enabled Source, per Worker Process.The 1 GB limit is on uncompressed inbound data, and no compression is applied to the queue. This limit is not configurable. For configurable queue size, compression, mode, and other options below, use a hybrid Group.
Enable Persistent Queue: Defaults to No. When toggled to Yes:
Mode: Select a condition for engaging persistent queues.
Always On: This default option will always write events to the persistent queue, before forwarding them to Cribl Stream’s data processing engine.Smart: This option will engage PQ only when the Source detects backpressure from Cribl Stream’s data processing engine.
Max buffer size: The maximum number of events to hold in memory before reporting backpressure to the sender and writing the queue to disk. Defaults to 1000. (This buffer is per connection, not just per Worker Process – and this can dramatically expand memory usage.)
Commit frequency: The number of events to send downstream before committing that Stream has read them. Defaults to 42.
Max file size: The maximum data volume to store in each queue file before closing it and (optionally) applying the configured Compression. Enter a numeral with units of KB, MB, etc. If not specified, Cribl Stream applies the default 1 MB.
Max queue size: The maximum amount of disk space that the queue is allowed to consume on each Worker Process. Once this limit is reached, this Source will stop queueing data and block incoming data. Required, and defaults to 5 GB. Accepts positive numbers with units of KB, MB, GB, etc. Can be set as high as 1 TB, unless you’ve configured a different Max PQ size per Worker Process in Group Settings.
Queue file path: The location for the persistent queue files. Defaults to $CRIBL_HOME/state/queues. To this field’s specified path, Cribl Stream will append /<worker-id>/inputs/<input-id>.
Compression: Optional codec to compress the persisted data after a file is closed. Defaults to None; Gzip is also available.
In Cribl Stream 4.1 and later, Source-side PQ’s default Mode is
Always on, to best ensure events’ delivery. For details on optimizing this selection, see Always On versus Smart Mode.You can optimize Workers’ startup connections and CPU load at Group Settings > Worker Processes.
Processing Settings
Event Breakers
This section defines event breaking rulesets that will be applied, in order, on the /raw endpoint.
Event Breaker rulesets: A list of event breaking rulesets that will be applied to the input data stream before the data is sent through the Routes. Defaults to System Default Rule.
Event Breaker buffer timeout: How long (in milliseconds) the Event Breaker will wait for new data to be sent to a specific channel, before flushing out the data stream, as-is, to the Routes. Minimum 10 ms, default 10000 (10 sec), maximum 43200000 (12 hours).
Fields
In this section, you can add Fields to each event using Eval-like functionality.
Name: Field name.
Value: JavaScript expression to determine field’s value (can be a constant).
Fields specified on the Fields tab will normally override fields of the same name in events. But you can specify that fields in events should override these fields’ values.
In particular, where incoming events have no
indexfield, this Source adds one with the literal valuedefault. You can override this value by using Add Field to specify anindexfield, and then setting its Value to an expression of the following form:index == 'default' ? 'myIndex' : indexFields here are evaluated and applied after any fields specified in the Auth Tokens section.
Pre-Processing
In this section’s Pipeline drop-down list, you can select a single existing Pipeline to process data from this input before the data is sent through the Routes.
Auth Tokens
If empty (the default), the Splunk HEC Source will permit client access without an auth token. To generate and/or configure tokens, click Add Token, which exposes the following fields:
Token: Shared secret to be provided by any client (Authorization: <token>). Click Generate to create a new secret. If empty, unauthenticated access will be permitted.
Enable token: Controls the status of the specified authentication token. When set to Yes, the specified auth token is active and can be used for client access. If it’s set to No, the token is disabled, causing it to be skipped and ignored during initialization. This means that any client attempting to use a disabled token will not be granted access.
Disabling a token can be helpful when you need to temporarily stop receiving data from a particular service or application. Disabling a token prevents the service or application from sending data to your endpoint without having to completely delete the token.
See also Periodic Logging for information on how auth tokens affect product logging.
Description: Optional description for this token.
Fields: Fields to add to events referencing this token. Each field is a Name/Value pair.
Fields specified on the Auth Tokens tab will normally override fields of the same name in events. But you can specify that fields in events should override these fields’ values.
In particular, where incoming events have no
indexfield, this Source adds one with the literal valuedefault. You can override this value by using Add Field to specify anindexfield, and then setting its Value to an expression of the following form:index == 'default' ? 'myIndex' : indexFields here are evaluated and applied before any fields specified in the Fields section.
Advanced Settings
Use Universal Forwarder time zone (S2S only): Leave the default toggle set to Yes to have Event Breakers determine the time zone for events based on Universal Forwarder–provided metadata when the time zone can’t be inferred from the raw event.
CORS allowed origins: If you need to enable cross-origin resource sharing with Splunk senders, use this field to specify the HTTP origins to which Cribl Stream should send Access-Control-Allow-* headers. You can enter multiple domains and use wildcards. This and its companion CORS allowed headers option should seldom be needed – see Working with CORS Headers below. Both options are available in Cribl Stream 4.1.2 and later.
CORS allowed headers: List HTTP headers that Cribl Stream will send in a CORS preflight response to your configured (above) CORS allowed origins as Access-Control-Allow-Headers. Enter * to allow all headers.
Enable proxy protocol: Toggle to Yes if the connection is proxied by a device that supports Proxy Protocol v1 or v2. This setting affects how the Source handles the __srcIpPort field.
Capture request headers: Toggle this to Yes to add request headers to events, in the __headers field.
Max active requests: Maximum number of active requests allowed for this Source, per Worker Process. Defaults to 256. Enter 0 for unlimited.
Activity log sample rate: Determines how often request activity is logged at the info level. The default 100 value logs every 100th value; a 1 value would log every request; a 10 value would log every 10th request; etc.
Max requests per socket: The maximum number of requests Cribl Stream should allow on one socket before instructing the client to close the connection. Defaults to 0 (unlimited). See Balancing Connection Reuse Against Request Distribution below.
Socket timeout (seconds): How long Cribl Stream should wait before assuming that an inactive socket has timed out. The default 0 value means wait forever.
Request timeout (seconds): How long to wait for an incoming request to complete before aborting it. The default 0 value means wait indefinitely.
Keep-alive timeout (seconds): After the last response is sent, Cribl Stream will wait this long for additional data before closing the socket connection. Defaults to 5 seconds; minimum is 1 second; maximum is 600 seconds (10 minutes).
The longer the Keep‑alive timeout, the more Cribl Stream will reuse connections. The shorter the timeout, the closer Cribl Stream gets to creating a new connection for every request. When request frequency is high, you can use longer timeouts to reduce the number of connections created, which mitigates the associated cost.
Environment: If you’re using GitOps, optionally use this field to specify a single Git branch on which to enable this configuration. If empty, the config will be enabled everywhere.
Balancing Connection Reuse Against Request Distribution
Max requests per socket allows you to limit the number of HTTP requests an upstream client can send on one network connection. Once the limit is reached, Cribl Stream uses HTTP headers to inform the client that it must establish a new connection to send any more requests. (Specifically, Cribl Stream sets the HTTP Connection header to close.) After that, if the client disregards what Cribl Stream has asked it to do and tries to send another HTTP request over the existing connection, Cribl Stream will respond with an HTTP status code of 503 Service Unavailable.
Use this setting to strike a balance between connection reuse by the client, and distribution of requests among one or more Worker Node processes by Cribl Stream:
When a client sends a sequence of requests on the same connection, that is called connection reuse. Because connection reuse benefits client performance by avoiding the overhead of creating new connections, clients have an incentive to maximize connection reuse.
Meanwhile, a single process on that Worker Node will handle all the requests of a single network connection, for the lifetime of the connection. When receiving a large overall set of data, Cribl Stream performs better when the workload is distributed across multiple Worker Node processes. In that situation, it makes sense to limit connection reuse.
There is no one-size-fits-all solution, because of variation in the size of the payload a client sends with a request and in the number of requests a client wants to send in one sequence. Start by estimating how long connections will stay open. To do this, multiply the typical time that requests take to process (based on payload size) times the number of requests the client typically wants to send.
If the result is 60 seconds or longer, set Max requests per socket to force the client to create a new connection sooner. This way, more data can be spread over more Worker Node processes within a given unit of time.
For example: Suppose a client tries to send thousands of requests over a very few connections that stay open for hours on end. By setting a relatively low Max requests per socket, you can ensure that the same work is done over more, shorter-lived connections distributed between more Worker Node processes, yielding better performance from Cribl Stream.
A final point to consider is that one Cribl Stream Source can receive requests from more than one client, making it more complicated to determine an optimal value for Max requests per socket.
Connected Destinations
Select Send to Routes to enable conditional routing, filtering, and cloning of this Source’s data via the Routing table.
Select QuickConnect to send this Source’s data to one or more Destinations via independent, direct connections.
Internal Fields
Cribl Stream uses a set of internal fields to assist in handling of data. These “meta” fields are not part of an event, but they are accessible, and Functions can use them to make processing decisions.
Fields for this Source:
__headers– Added only when Advanced Settings > Capture request headers is set toYes.__hecToken__inputId__s2sVersion– value can be eitherv3orv4. This field is present only when the Source is receiving S2S-encoded payloads.__srcIpPort– See details below.__TZ
Universal Forwarder Time Zone
The
__TZfield uses the universal forwarder time zone to mitigate cases where incoming events have timestamp strings but no time zone information. Event Breakers use the__TZfield to derive time zone information, enabling them to set the_timefield correctly. See Using the UF Time Zone for additional information.
Overriding __srcIpPort with Client IP/Port
The __srcIpPort field’s value contains the IP address and (optionally) port of the Splunk HEC client sending data to this Source.
When any proxies (including load balancers) lie between the Splunk HEC client and the Source, the last proxy adds an X‑Forwarded‑For header whose value is the IP/port of the original client. With multiple proxies, this header’s value will be an array, whose first item is the original client IP/port.
If X‑Forwarded‑For is present, and Advanced Settings > Enable proxy protocol is set to No, the original client IP/port in this header will override the value of __srcIpPort.
If Enable proxy protocol is set to Yes, the X‑Forwarded‑For header’s contents will not override the __srcIpPort value. (Here, the upstream proxy can convey the client IP/port without using this header.)
Working with CORS Headers
The CORS allowed origins and CORS allowed headers settings are needed only when you want JavaScript code running in a web browser to send events to the Splunk HEC Source. In this (uncommon) scenario, the code in question sends a preflight request that includes CORS (Cross-Origin Resource Sharing) headers, and the Splunk HEC Source includes CORS headers in its response.
If the settings (and thus the CORS headers in the response) are correct, the browser will allow the code in question to complete requests to the Splunk HEC Source – that is, allow the code to read the Source’s responses. (These settings are optional because for some web applications it’s sufficient to send requests without reading responses.)
The CORS header dance begins when the web browser sends a request with a header stating its origin. What happens next depends on how you’ve configured the CORS header settings, as explained in the tables below. (For these examples, we’ll assume an origin of https://mycoolwebapp:3001.)
| CORS allowed origins value | What Splunk HEC Source does | Does Browser then allow code to read response? |
|---|---|---|
* | Send Access-Control-Allow-Origin: * header. | Yes |
| Multiple wildcard values | If origin value matches any wildcard, send Access-Control-Allow-Origin: https://mycoolwebapp:3001 header. | Yes |
| Nothing (not configured) | Send neither an Access-Control-Allow-Origin nor an Access-Control-Allow-Headers header. | No |
The web browser’s request might also include an Access-Control-Request-Headers header that lists one or more headers that it wants to use in a subsequent POST request (that is, the “actual” as opposed to preflight request). The Splunk HEC Source can then respond with an Access-Control-Allow-Headers header if and only if it’s also sending the Access-Control-Allow-Origin header.
| CORS allowed headers value | What Splunk HEC Source does | Does Browser then allow code to read response? |
|---|---|---|
* | Send Access-Control-Allow-Headers header with the same list the client sent. | Yes |
| Multiple wildcard values | If any headers from the client’s list match wildcards, send Access-Control-Allow-Headers header listing the matching headers. | Yes |
| Nothing (not configured) | Do not send an Access-Control-Allow-Headers header. | Probably not |
Format and Endpoint Examples
Splunk HEC to Cribl Stream
- Configure Cribl Stream to listen on port
8088with an auth token ofmyToken42. - Send a payload to your Cribl Stream receiver.
Note: Token specification can be either Splunk <token> or <token>.
curl -k http://<myCriblHost>:8088/services/collector/event -H 'Authorization: myToken42' -d '{"event":"this is a sample event ", "host":"myHost", "source":"mySource", "fieldA":"valueA", "fieldB":"valueB"}'
curl -k http://<myCriblHost>:8088/services/collector -H 'Authorization: myToken42' -d '{"event":"this is a sample event ", "host":"myHost", "source":"mySource", "fieldA":"valueA", "fieldB":"valueB"}'
# Multiple Events
curl -k http://<myCriblHost>:8088/services/collector -H 'Authorization: myToken42' -d '{"event":"this is a sample event ", "host":"myHost", "source":"mySource", "fieldA":"valueA", "fieldB":"valueB"}{"event":"this is a sample event 2", "host":"myHost", "source":"mySource", "fieldA":"valueA", "fieldB":"valueB"}'
# Metrics Events
curl -k http://<myCriblHost>:8088/services/collector/event -H 'Authorization: myToken42' -d '{"event":"metric", "host":"myHost", "fields":{"_value":3850,"metric_name":"kernel.entropy_avail"}}'
curl -k http://<myCriblHost>:8088/services/collector/event -H 'Authorization: myToken42' -d '{"host":"myHost", "fields":{"_value":3850,"metric_name":"kernel.entropy_avail"}}'
# Send the auth token as a query parameter, with no additional configuration
curl -k "http://<myCriblHost>:8088/services/collector/event?token=mToken42" -d '{"event":"this is a sample event ", "host":"myHost", "source":"mySource", "fieldA":"valueA", "fieldB":"valueB"}'curl -k http://<myCriblHost>:8088/services/collector/raw -H 'Authorization: myToken42' -d '<146>Jul 2 08:40:30 tpapigw02 c2b_server_1: APIGW-C2B: timestamp="07.02.2021 08:40:30,968" ip="10.88.157.144" filterType="ChangeMessageFilter"'# Health Events
curl -k https://<myCriblHost>:8088/services/collector/healthSplunk HEC to Cribl.Cloud
- Navigate to Cribl.Cloud’s Splunk HEC Source > Auth Tokens tab.
- Copy your token out of the Token field.
- From the command line, use
https, your Cribl.Cloud portal’s Ingest Address and port, and the token’s value. You can find the Ingest Address on the top nav’s Network Settings page, under the Data Sources tab.
curl -k "https://default.main-<Your-Org-ID>.cribl.cloud:8088/services/collector" \
-H "Authorization: <token_value>" \
-d '{"event": "Goats are better than ponies."}{"event": "Goats are better climbers."}{"event": "Goats are great yoga buddies.", "nested": {"horns": "Two is better than one!"}}'With a Cribl.Cloud Enterprise plan, generalize the above URL’s
default.mainsubstring to<group-name>.mainwhen sending to other Worker Groups.
Periodic Logging
Cribl Stream logs metrics about incoming requests and ingested events once per minute.
If one or more auth tokens are configured and enabled, Cribl Stream logs requests and events for each enabled auth token individually. Since the tokens themselves are redacted for security, Cribl Stream logs the initial text of the token description to help you identify which token a given log is for.
If no auth token is configured and enabled, Cribl Stream simply logs overall statistics about incoming requests and ingested events.
These logs are stored in the metrics.log file. To view them in the UI, open the Source’s Logs tab and choose Worker Process X Metrics from the drop-down, where X is the desired Worker process.