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1# Apache Kafka {#module-services-apache-kafka}
2
3[Apache Kafka](https://kafka.apache.org/) is an open-source distributed event
4streaming platform
5
6## Basic Usage {#module-services-apache-kafka-basic-usage}
7
8The Apache Kafka service is configured almost exclusively through its
9[settings](#opt-services.apache-kafka.settings) option, with each attribute
10corresponding to the [upstream configuration
11manual](https://kafka.apache.org/documentation/#configuration) broker settings.
12
13## KRaft {#module-services-apache-kafka-kraft}
14
15Unlike in Zookeeper mode, Kafka in
16[KRaft](https://kafka.apache.org/documentation/#kraft) mode requires each log
17dir to be "formatted" (which means a cluster-specific a metadata file must
18exist in each log dir)
19
20The upstream intention is for users to execute the [storage
21tool](https://kafka.apache.org/documentation/#kraft_storage) to achieve this,
22but this module contains a few extra options to automate this:
23
24- [](#opt-services.apache-kafka.clusterId)
25- [](#opt-services.apache-kafka.formatLogDirs)
26- [](#opt-services.apache-kafka.formatLogDirsIgnoreFormatted)
27
28## Migrating to settings {#module-services-apache-kafka-migrating-to-settings}
29
30Migrating a cluster to the new `settings`-based changes requires adapting removed options to the corresponding upstream settings.
31
32This means that the upstream [Broker Configs documentation](https://kafka.apache.org/documentation/#brokerconfigs) should be followed closely.
33
34Note that dotted options in the upstream docs do _not_ correspond to nested Nix attrsets, but instead as quoted top level `settings` attributes, as in `services.apache-kafka.settings."broker.id"`, *NOT* `services.apache-kafka.settings.broker.id`.
35
36Care should be taken, especially when migrating clusters from the old module, to ensure that the same intended configuration is reproduced faithfully via `settings`.
37
38To assist in the comparison, the final config can be inspected by building the config file itself, ie. with: `nix-build <nixpkgs/nixos> -A config.services.apache-kafka.configFiles.serverProperties`.
39
40Notable changes to be aware of include:
41
42- Removal of `services.apache-kafka.extraProperties` and `services.apache-kafka.serverProperties`
43 - Translate using arbitrary properties using [](#opt-services.apache-kafka.settings)
44 - [Upstream docs](https://kafka.apache.org/documentation.html#brokerconfigs)
45 - The intention is for all broker properties to be fully representable via [](#opt-services.apache-kafka.settings).
46 - If this is not the case, please do consider raising an issue.
47 - Until it can be remedied, you *can* bail out by using [](#opt-services.apache-kafka.configFiles.serverProperties) to the path of a fully rendered properties file.
48
49- Removal of `services.apache-kafka.hostname` and `services.apache-kafka.port`
50 - Translate using: `services.apache-kafka.settings.listeners`
51 - [Upstream docs](https://kafka.apache.org/documentation.html#brokerconfigs_listeners)
52
53- Removal of `services.apache-kafka.logDirs`
54 - Translate using: `services.apache-kafka.settings."log.dirs"`
55 - [Upstream docs](https://kafka.apache.org/documentation.html#brokerconfigs_log.dirs)
56
57- Removal of `services.apache-kafka.brokerId`
58 - Translate using: `services.apache-kafka.settings."broker.id"`
59 - [Upstream docs](https://kafka.apache.org/documentation.html#brokerconfigs_broker.id)
60
61- Removal of `services.apache-kafka.zookeeper`
62 - Translate using: `services.apache-kafka.settings."zookeeper.connect"`
63 - [Upstream docs](https://kafka.apache.org/documentation.html#brokerconfigs_zookeeper.connect)