Add sysctl (#138)

Signed-off-by: Christian Berendt <[email protected]>

docs/guides/configuration-guides/commons/sysctl.md

@@ -0,0 +1,36 @@
+---
+sidebar_label: Sysctl
+---
+
+# Sysctl
+
+With the `osism.commons.sysctl` role, it is possible to manage the attributes of the kernel
+via [sysctl](https://en.wikipedia.org/wiki/Sysctl) on a node.
+
+The following defaults are set via the parameter `sysctl_defaults`.
+
+**Group**                    | **Attribute**                          | **Default**
+-----------------------------|----------------------------------------|---------------------
+elasticsearch                | vm.max_map_count                       | 262144
+rabbitmq                     | net.ipv4.tcp_keepalive_time            | 6
+rabbitmq                     | net.ipv4.tcp_keepalive_intvl           | 3
+rabbitmq                     | net.ipv4.tcp_keepalive_probes          | 3
+rabbitmq                     | net.core.wmem_max                      | 16777216
+rabbitmq                     | net.core.rmem_max                      | 16777216
+rabbitmq                     | net.ipv4.tcp_fin_timeout               | 20
+rabbitmq                     | net.ipv4.tcp_tw_reuse                  | 1
+rabbitmq                     | net.core.somaxconn                     | 4096
+rabbitmq                     | net.ipv4.tcp_syncookies                | 0
+rabbitmq                     | net.ipv4.tcp_max_syn_backlog           | 8192
+generic                      | vm.swappiness                          | 1
+compute                      | net.netfilter.nf_conntrack_max         | 1048576
+
+The `sysctl_extra` parameter can be used to set your own parameters or overwrite existing
+parameters in the defaults.
+
+```yaml title="Set attribute fs.inotify.max_user_instances to 256 for all nodes in group generic"
+sysctl_extra:
+  generic:
+    - name: fs.inotify.max_user_instances
+      value: 256
+```