How It Works

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You can use the Cribl TCP Destination to transfer data between Worker Nodes and Workers. If the Cribl TCP Destination sends data to its Cribl TCP Source counterpart on another Worker, you’re billed for ingress only once – when Cribl first receives the data. All data subsequently relayed to other Workers via a Cribl TCP Destination/Source pair is not charged.

This use case is common in hybrid Cribl.Cloud deployments, where a customer-managed (hybrid) Worker Node sends data to a Worker in Cribl.Cloud for additional processing and routing to Destinations. However, the Cribl TCP Destination/Source pair can similarly reduce your metered data ingress in other scenarios, such as on-prem Cribl Edge to on-prem Cribl Stream.

As one usage example, assume that you want to send data from one Node deployed on-prem, to another that is deployed in Cribl.Cloud. You could do the following:

• Create an on-prem File System Collector (or whatever Collector or Source is suitable) for the data you want to send to Cribl.Cloud.
• Create an on-prem Cribl TCP Destination.
• Create a Cribl TCP Source, on the target Cribl Stream Worker Group or Cribl Edge Fleet in Cribl.Cloud.
• For an on-prem Node configure a File System Collector to send data to the Cribl TCP Destination, and from there to the Cribl TCP Source in Cribl.Cloud.
• On Cribl-managed Nodes in Cribl.Cloud, make sure that TLS is either disabled on both the Cribl TCP Destination and the Cribl TCP Source it’s sending data to, or enabled on both. Otherwise, no data will flow. On Cribl.Cloud instances, the Cribl TCP Source ships with TLS enabled by default.

Configuration Requirements

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The key points about configuring this architecture are:

• The Cribl TCP Destination must be on a Node that is connected to the same Leader as the Cribl TCP Source.
• When you configure the Cribl TCP Destination, its Address and Port values must point to the Address and Port you’ve configured on the Cribl TCP Source.
• Cribl 3.5.4 was a breakpoint in Cribl TCP Leader/Worker communications. Nodes running the Cribl TCP Source on Cribl 3.5.4 and later can send data only to Nodes running v.3.5.4 and later. Nodes running the Cribl TCP Source on Cribl 3.5.3 and earlier can send data only to Nodes running v.3.5.3 and earlier.

Configure a Cribl TCP Destination

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1. On the top bar, select Products, and then select Cribl Stream. Under Worker Groups, select a Worker Group. Next, you have two options:
   • To configure via QuickConnect, navigate to Routing > QuickConnect (Stream) or Collect (Edge). Select Add Destination and select the Destination you want from the list, choosing either Select Existing or Add New.
   • To configure via the Routes, select Data > Destinations or More > Destinations (Edge). Select the Destination you want. Next, select Add Destination.
2. In the New Destination modal, configure the following under General Settings:

   • Output ID: Enter a unique name to identify this Destination definition. If you clone this Destination, Cribl Stream will add -CLONE to the original Output ID.

   • Description: Optionally, enter a description.

   • Load balancing: When toggled on, see Load Balancing Settings below.

     The following two fields appear only if Load balancing is toggled off (default), and must match the Address and Port you’ve configured on the peer Cribl TCP Source to which you’re sending.

   • Address: Hostname of the receiver.

   • Port: Port number to connect to on the host, for example, 10300.

3. Next, you can configure the following Optional Settings:
   • Compression: Codec to use to compress the data before sending. Defaults to Gzip.
   • Throttling: Throttle rate, in bytes per second. Defaults to 0, meaning no throttling. Multiple-byte units such as KB, MB, and so forth, are also allowed – for example, 42 MB. When throttling is engaged, your Backpressure behavior selection determines whether Cribl Stream will handle excess data by blocking it, dropping it, or queueing it to disk. When used in conjunction with Max connections, the throttling rate is applied per connection. For instance, if Max connections is set to 2 and throttling is set to 3 MB, each of the two connections can send data at a rate of up to 3 MB per second, resulting in a total potential throughput of 6 MB per second across both connections.
   • Backpressure behavior: Specifies whether to block, drop, or queue events when all receivers are exerting backpressure. Defaults to Block. See Persistent Queue Settings below.
   • Tags: Optionally, add tags that you can use to filter and group Destinations on the Destinations page. These tags aren’t added to processed events. Use a tab or hard return between (arbitrary) tag names.
4. Optionally, configure any TLS settings, Persistent Queue, Timeout, Processing, and Advanced settings outlined in the sections below.
5. Select Save, then Commit & Deploy.

Load Balancing Settings

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Enabling the Load balancing toggle displays the following controls:

Exclude Current Host IPs

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Displays under Optional Setting when Load balancing is toggled on. This toggle determines whether to exclude all IPs of the current host from the list of any resolved hostnames. Default is toggled off, which keeps the current host available for load balancing.

Destinations

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The Destinations table is where you specify a set of receivers on which to load-balance data. Click Add Destination to specify more receivers on new rows. Each row provides the following fields:

Address: Hostname of a receiver. Optionally, you can paste in a comma-separated list, in <host>:<port> format.

Port: Port number to send data to on the host.

Each Address/Port combination must match the Address and Port configured on a peer TCP Source to which you’re sending.

TLS: Whether to inherit TLS configs from group setting, or disable TLS. Defaults to inherit.

TLS servername: Servername to use if establishing a TLS connection. If not specified, defaults to connection host (if not an IP); otherwise, uses the global TLS settings.

Load weight: Set the relative traffic-handling capability for each connection by assigning a weight (> 0). This column accepts arbitrary values, but for best results, assign weights in the same order of magnitude to all connections. Cribl Stream will attempt to distribute traffic to the connections according to their relative weights.

The final column provides an X button to delete any row from the table.

For details on configuring all these options, see About Load Balancing.

Persistent Queue Settings

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The Persistent Queue Settings tab displays when the Backpressure behavior option in General settings is set to Persistent Queue. Persistent queue buffers and preserves incoming events when a downstream Destination has an outage or experiences backpressure.

Before enabling persistent queue, learn more about persistent queue behavior and how to optimize it with your system:

• About Persistent Queues
• Optimize Destination Persistent Queues (dPQ)
• Destination Backpressure Triggers

On Cribl-managed Cloud Workers (with an Enterprise plan), this tab exposes only the destructive Clear Persistent Queue button (described at the end of this section). A maximum queue size of 1 GB disk space is automatically allocated per PQ‑enabled Destination, per Worker Process. The 1 GB limit is on outbound uncompressed data, and no compression is applied to the queue.

This limit is not configurable. If the queue fills up, Cribl Stream/Edge will block outbound data. To configure the queue size, compression, queue-full fallback behavior, and other options below, use a hybrid Group.

Mode: Use this menu to select when Cribl Stream/Edge engages the persistent queue in response to backpressure events from this Destination. The options are:

If a Worker/Edge Node starts with an invalid Mode setting, it automatically switches to Error mode. This might happen if the Worker/Edge Node is running a version that does not support other modes (older than 4.9.0), or if it encounters a nonexistent value in YAML configuration files.

File size limit: The maximum data volume to store in each queue file before closing it. Enter a numeral with units of KB, MB, etc. Defaults to 1 MB.

Max queue size: The maximum amount of disk space that the queue can consume on each Worker Process. When the queue reaches this limit, the Destination stops queueing data and applies the Queue‑full behavior. Defaults to 5 GB. This field accepts positive numbers with units of KB, MB, GB, and so on. You can set it as high as 1 TB, unless you’ve configured a different Worker Process PQ size limit on the Group Settings/Fleet Settings page.

Queue file path: The location for the persistent queue files. Defaults to $CRIBL_HOME/state/queues. Cribl Stream/Edge will append /<worker‑id>/<output‑id> to this value.

Compression: Set the codec to use when compressing the persisted data after closing a file. Defaults to None. Gzip is also available.

Queue-full behavior: Whether to block or drop events when the queue begins to exert backpressure. A queue begins to exert backpressure when the disk is low or at full capacity. This setting has two options:

• Block: The output will refuse to accept new data until the receiver is ready. The system will return block signals back to the sender.
• Drop new data: Discard all new events until the backpressure event has resolved and the receiver is ready.

Backpressure duration Limit: When Mode is set to Backpressure, this setting controls how long to wait during network slowdowns before activating queues. A shorter duration enhances critical data loss prevention, while a longer duration helps avoid unnecessary queue transitions in environments with frequent, brief network fluctuations. The default value is 30 seconds.

Strict ordering: Toggle on (default) to enable FIFO (first in, first out) event forwarding, ensuring Cribl Stream/Edge sends earlier queued events first when receivers recover. The persistent queue flushes every 10 seconds in this mode. Toggle off to prioritize new events over queued events, configure a custom drain rate for the queue, and display this option:

• Drain rate limit (EPS): Optionally, set a throttling rate (in events per second) on writing from the queue to receivers. (The default 0 value disables throttling.) Throttling the queue drain rate can boost the throughput of new and active connections by reserving more resources for them. You can further optimize Worker startup connections and CPU load in the Worker Processes settings.

Clear Persistent Queue: For Cloud Enterprise only, click this button if you want to delete the files that are currently queued for delivery to this Destination. If you click this button, a confirmation modal appears. Clearing the queue frees up disk space by permanently deleting the queued data, without delivering it to downstream receivers. This button only appears after you define the Output ID.

Use the Clear Persistent Queue button with caution to avoid data loss. See Steps to Safely Disable and Clear Persistent Queues for more information.

TLS Settings (Client Side)

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Use TLS: Defaults to toggled off. When toggled on:

Autofill?: This setting is experimental.

Validate server certs: Reject certificates that are not authorized by a CA in the CA certificate path, or by another trusted CA (for example, the system’s CA). Default is toggled off.

Server name (SNI): Server name for the SNI (Server Name Indication) TLS extension. This must be a host name, not an IP address.

Minimum TLS version: Optionally, select the minimum TLS version to use when connecting.

Maximum TLS version: Optionally, select the maximum TLS version to use when connecting.

Certificate name: The name of the predefined certificate.

CA certificate path: Path on client containing CA certificates (in PEM format) to use to verify the server’s cert. Path can reference $ENV_VARS.

Private key path (mutual auth): Path on client containing the private key (in PEM format) to use. Path can reference $ENV_VARS. Use only if mutual auth is required.

Certificate path (mutual auth): Path on client containing certificates in (PEM format) to use. Path can reference $ENV_VARS. Use only if mutual auth is required.

Passphrase: Passphrase to use to decrypt private key.

Timeout Settings

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Connection timeout: Amount of time (in milliseconds) to wait for the connection to establish before retrying. Defaults to 10000.

Write timeout: Amount of time (in milliseconds) to wait for a write to complete before assuming connection is dead. Defaults to 60000.

Processing Settings

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Post‑Processing

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Pipeline: Pipeline or Pack to process data before sending the data out using this output.

System fields: A list of fields to automatically add to events that use this output. By default, includes cribl_pipe (identifying the Cribl Stream Pipeline that processed the event). Supports wildcards. Other options include:

• cribl_host – Cribl Stream Node that processed the event.
• cribl_input – Cribl Stream Source that processed the event.
• cribl_output – Cribl Stream Destination that processed the event.
• cribl_route – Cribl Stream Route (or QuickConnect) that processed the event.
• cribl_wp – Cribl Stream Worker Process that processed the event.

Advanced Settings

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Auth Token TTL minutes: The number of minutes before the internally generated authentication token expires, valid values between 1 and 60.

Exclude fields: Fields to exclude from the event. This Destination excludes __kube_*, __metadata, and __winEvent by default and forwards all other Internal Fields. For more information about __winEvent, see the Windows Event Logs Source topic.

If you are running Cribl Stream 4.0.x (or earlier) and are using the Kubernetes Metrics Source with this Destination, consider excluding the following fields to reduce event size:

!__inputId,!__outputId,!__criblMetrics,__* .

The contents of __raw are often redundant with the _raw field’s contents. Where they are identical, consider excluding one of the two.

Log failed requests to disk: Toggling on makes the payload of the most recently failed request available for inspection. See Inspect Payload to Troubleshoot Closed Connections below.

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.

The following options are added if you enable the General Settings tab’s Load balancing option:

DNS resolution period (seconds): Re-resolve any hostnames after each interval of this many seconds, and pick up destinations from A records. Defaults to 600 seconds.

Load balance stats period (seconds): Lookback traffic history period. Defaults to 300 seconds. (Note that If multiple receivers are behind a hostname – i.e., multiple A records – all resolved IPs will inherit the weight of the host, unless each IP is specified separately. In Cribl Stream load balancing, IP settings take priority over those from hostnames.)

Max connections: Constrains the number of concurrent receiver connections, per Worker Process, to limit memory utilization. If set to a number > 0, then on every DNS resolution period, Cribl Stream will randomly select this subset of discovered IPs to connect to. Cribl Stream will rotate IPs in future resolution periods – monitoring weight and historical data, to ensure fair load balancing of events among IPs.

Inspect Payload to Troubleshoot Closed Connections

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When a downstream receiver closes connections from this Destination (or just stops responding), inspecting the payload of the most recently failed request can help you find the cause. For example:

• Suppose you send an event whose size is larger than the downstream receiver can handle.
• Suppose you send an event that has a number field, but the value exceeds the highest number that the downstream receiver can handle.

When Log failed requests to disk is enabled, you can inspect the last failed request payload. Here is how:

1. In the Destination UI, navigate to the Logs tab.
2. Find a log entry with a connection error message.
3. Expand the log entry.
4. If the message includes the phrase See payload file for more info, note the path in the file field on the next line.

Now you have the path to the directory where Cribl Stream is storing the payload from the last failed request.

Internal Fields Loopback to Sources

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The Cribl TCP and Cribl HTTP Destinations differ from all other Destinations in the way they handle internal fields: They normally send data back to their respective Cribl Sources – where Cribl internal fields, metrics, and sender-generated fields can all be useful.

These Destinations forward all internal fields by default, except for any that you exclude in Advanced Settings > Exclude fields.

As examples, if the following fields are present on an event forwarded by a Cribl HTTP or Cribl TCP Destination, they’ll be accessible in the ingesting Cribl HTTP/TCP Source:__criblMetrics, __srcIpPort, __inputId, and __outputId.