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micheleRP merged 17 commits into from
Sep 17, 2025
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DOC-1643 single source client connections in docs #1357

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DOC-1643 single source client connections in docs
micheleRP Sep 15, 2025
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24 changes: 23 additions & 1 deletion modules/manage/pages/cluster-maintenance/configure-availability.adoc
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@@ -1,6 +1,7 @@
= Configure Client Connections
:description: Guidelines for configuring Redpanda clusters for optimal availability.
:page-categories: Management, Networking
// tag::single-source[]

Optimize the availability of your clusters by configuring and tuning properties.

Expand All @@ -10,14 +11,16 @@ A malicious Kafka client application may create many network connections to exec

The following Redpanda cluster properties limit the number of connections:

* xref:reference:cluster-properties.adoc#kafka_connections_max[`kafka_connections_max`]: Similar to Kafka's `max.connections`, this sets the maximum number of connections per broker.
* xref:reference:cluster-properties.adoc#kafka_connections_max_per_ip[`kafka_connections_max_per_ip`]: Similar to Kafka's `max.connections.per.ip`, this sets the maximum number of connections accepted per IP address by a broker.
* xref:reference:cluster-properties.adoc#kafka_connections_max_overrides[`kafka_connections_max_overrides`]: A list of IP addresses for which `kafka_connections_max_per_ip` is overridden and doesn't apply.
ifndef::env-cloud[]
* xref:reference:cluster-properties.adoc#kafka_connections_max[`kafka_connections_max`]: Similar to Kafka's `max.connections`, this sets the maximum number of connections per broker.

Redpanda also provides properties to manage the rate of connection creation:

* xref:reference:cluster-properties.adoc#kafka_connection_rate_limit[`kafka_connection_rate_limit`]: This property limits the maximum rate of connections created per second. It applies to each CPU core.
* xref:reference:cluster-properties.adoc#kafka_connection_rate_limit_overrides[`kafka_connection_rate_limit_overrides`]: A list of IP addresses for which `kafka_connection_rate_limit` is overridden and doesn't apply.
endif::[]

[NOTE]
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@mattschumpert mattschumpert Sep 15, 2025

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@travisdowns is the note below accurate about connections counts? 'Typically two or three' sounds just wrong. Doesn't a client open a connection for each broker its connected to (or for each partition its producing/consuming to/from).

Its good to first note that num connections != num clients, but I think the message here is the max expected # of connections per client is 'on the order of [insert something]'

cc @micheleRP

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@travisdowns travisdowns Sep 17, 2025

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Yes, 2 or 3 would be a large underestimate if there are many brokers, and if clients connect to each broker (which is workload dependent).

Here are the full details:

https://redpandadata.atlassian.net/wiki/spaces/CORE/pages/510099463/How+many+connections

That's probably not going to make it into this paragraph, but a conservative estimate is N+2 connections per client where N is the number of brokers.

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@micheleRP micheleRP Sep 17, 2025 •
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Thank you @travisdowns! I changed that bullet (typically 2-3 connections per client) to:
The total number of connections is not equal to the number of clients, because a client can open multiple connections. As a conservative estimate, for a cluster with N brokers, plan for N + 2 connections per client.

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@travisdowns travisdowns Sep 17, 2025

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LGTM.

====
Expand Down Expand Up @@ -46,10 +49,21 @@ See also: xref:develop:produce-data/configure-producers.adoc[Configure Producers

A Redpanda broker may create log segments at startup. If a broker crashes after startup, and if it gets stuck in a crash loop, it could produce progressively more stored state that uses more disk space and takes more time for each restart to process.

ifndef::env-cloud[]
To prevent infinite crash loops, the Redpanda broker property xref:reference:node-properties.adoc#crash_loop_limit[`crash_loop_limit`] sets an upper limit on the number of consecutive crashes that can happen within one hour of each other. After it reaches the limit, a broker cannot restart until its internal consecutive crash counter is reset to zero by one of the following conditions:
endif::[]

ifdef::env-cloud[]
To prevent infinite crash loops, the Redpanda broker property [`crash_loop_limit`] sets an upper limit on the number of consecutive crashes that can happen within one hour of each other. After it reaches the limit, a broker cannot restart until its internal consecutive crash counter is reset to zero by one of the following conditions:
endif::[]

* The `redpanda.yaml` configuration file is updated.
ifndef::env-cloud[]
* The `startup_log` file in the broker's xref:reference:node-properties.adoc#data_directory[data_directory] is manually deleted.
endif::[]
ifdef::env-cloud[]
* The `startup_log` file in the broker's `data_directory` is manually deleted.
endif::[]
* One hour has elapsed since the last crash.
* The broker is properly shut down. (This is not possible after `crash_loop_limit` has been reached and the broker cannot be restarted.)

Expand All @@ -59,4 +73,12 @@ To prevent infinite crash loops, the Redpanda broker property xref:reference:nod
* If the limit is less than two, the broker is blocked from restarting after every crash, until one of the reset conditions is met.
====

ifndef::env-cloud[]
To facilitate debugging in environments where a broker is stuck in a crash loop, set the xref:reference:properties/broker-properties.adoc#crash_loop_sleep_sec[`crash_loop_sleep_sec` configuration]. This setting determines how long the broker sleeps before terminating the process after reaching the crash loop limit. The window during which the broker remains available allows you to troubleshoot the issue. This setting is most useful when xref:troubleshoot:errors-solutions/k-resolve-errors.adoc[troubleshooting in Kubernetes environments].
endif::[]

ifdef::env-cloud[]
To facilitate debugging in environments where a broker is stuck in a crash loop, set the `crash_loop_sleep_sec` configuration. This setting determines how long the broker sleeps before terminating the process after reaching the crash loop limit. The window during which the broker remains available allows you to troubleshoot the issue.
endif::[]

// end::single-source[]
11 changes: 11 additions & 0 deletions modules/reference/pages/properties/cluster-properties.adoc
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Expand Up @@ -2862,6 +2862,7 @@ Maximum number of Kafka client connections per broker. If `null`, the property i

---

// tag::kafka_connections_max_overrides[]
=== kafka_connections_max_overrides

A list of IP addresses for which Kafka client connection limits are overridden and don't apply. For example, `(['127.0.0.1:90', '50.20.1.1:40']).`.
Expand All @@ -2872,14 +2873,20 @@ A list of IP addresses for which Kafka client connection limits are overridden a

*Type:* array

ifndef::env-cloud[]
*Default*: `{}` (empty list)
endif::[]

*Related topics*:

* xref:manage:cluster-maintenance/configure-availability.adoc#limit-client-connections[Limit client connections]

---


// end::kafka_connections_max_overrides[]

// tag::kafka_connections_max_per_ip[]
=== kafka_connections_max_per_ip

Maximum number of Kafka client connections per IP address, per broker. If `null`, the property is disabled.
Expand All @@ -2892,14 +2899,18 @@ Maximum number of Kafka client connections per IP address, per broker. If `null`

*Accepted values:* [`0`, `4294967295`]

ifndef::env-cloud[]
*Default:* `null`
endif::[]

*Related topics*:

* xref:manage:cluster-maintenance/configure-availability.adoc#limit-client-connections[Limit client connections]

---

// end::kafka_connections_max_per_ip[]

=== kafka_enable_authorization

Flag to require authorization for Kafka connections. If `null`, the property is disabled, and authorization is instead enabled by <<enable_sasl,`enable_sasl`>>.
Expand Down