Add redis maxmemmory calculation and change the parameter in the redis.conf accordingly

docs/redis_guide.md

@@ -107,6 +107,9 @@ The following tables lists the default variables located in `roles/redis/default
 | `redis_bind_addr_source` | String | The bind address source. Will default to the Ansible `inventory_hostname` unless explicitly set to `default_ipv4_address`. | `inventory_hostname` |
 | `redis_bind_addrs` | String | A space-separated list of hostnames/IP addresses on which Redis listeners will be created. If `redis_bind_ipv6` is set to `true`, `::1` will be added to the addresses. The `redis_bind_addr_source` will also be added to the addresses. | `127.0.0.1` |
 | `redis_tls_enabled` | Boolean | Flag to enable TLS connections. | `false` |
+| `redis_maxmemory_bytes` | Integer | Maximum memory Redis can use (maxmemory). When set to auto, the installer calculates the value from the system RAM using: `maxmemory = max(redis_maxmemory_min_mb, system_ram × redis_maxmemory_ratio)`. If a numeric value is provided, that value (in bytes) is used directly and the automatic calculation is skipped. | `auto` |
+| `redis_maxmemory_ratio` | Float | Define how much memory the system will use. Only work if `redis_maxmemory_bytes` is configured as auto. Default value 0.6 means 60%. | `0.60` |
+| `redis_maxmemory_min_mb` | Integer | This parameter defines the minimum amount of memory Redis is allowed to use, even if the automatic calculation would result in a smaller value. It acts as a safety floor for the maxmemory calculation. | `512` |
 
 ### Auth Variables
 

roles/redis/defaults/main/redis.yml

@@ -61,3 +61,13 @@ redis_user_repluser_password: repluser
 redis_user_sentineladmin_password: admin
 redis_user_sentineluser_password: sentineluser
 redis_user_prometheus_password: prometheus
+
+# Redis memory sizing defaults (dedicated Redis node)
+
+# If set to "auto", maxmemory is calculated from system RAM.
+# If set to a number (bytes), that value is used verbatim.
+redis_maxmemory_bytes: auto
+
+# Used only when redis_maxmemory_bytes == "auto"
+redis_maxmemory_ratio: 0.60
+redis_maxmemory_min_mb: 512

roles/redis/tasks/configure-redis.yml

@@ -9,6 +9,49 @@
     group: root
     mode: "0644"
 
+# Calculate the Redis maxmemory value automatically when the parameter
+# `redis_maxmemory_bytes` is set to "auto".
+#
+# The calculation uses the following formula:
+#
+#   maxmemory = max(redis_maxmemory_min_mb, system_ram × redis_maxmemory_ratio)
+#
+# Where:
+#   system_ram               -> Total system memory detected by Ansible (in MB)
+#   redis_maxmemory_ratio    -> Percentage of system memory Redis is allowed to use
+#   redis_maxmemory_min_mb   -> Minimum memory Redis should be assigned
+#
+# The `max()` function ensures Redis always receives at least the configured
+# minimum memory, even on small systems.
+#
+# The final value is converted from MB to bytes because Redis expects the
+# `maxmemory` configuration parameter to be expressed in bytes.
+#
+# Example (10 GB system):
+#   system_ram = 10240 MB
+#   ratio = 0.60
+#   result = 6144 MB
+#   redis_maxmemory_bytes = 6442450944
+#
+# If `redis_maxmemory_bytes` is set to a numeric value instead of "auto",
+# this calculation is skipped and the provided value is used directly.
+- name: Calculate Redis maxmemory automatically
+  ansible.builtin.set_fact:
+    redis_maxmemory_bytes: >-
+      {{
+        (
+          [
+            redis_maxmemory_min_mb | int,
+            (
+              (ansible_facts.memtotal_mb | int)
+              * (redis_maxmemory_ratio | float)
+            ) | int
+          ] | max
+        ) * 1024 * 1024
+      }}
+  when: redis_maxmemory_bytes == "auto"
+  tags: configure_redis
+
 - name: Use template to generate redis.conf
   ansible.builtin.template:
     src: redis.conf.j2

roles/redis/templates/redis.conf.j2

@@ -1035,7 +1035,7 @@ acllog-max-len 128
 # limit for maxmemory so that there is some free RAM on the system for replica
 # output buffers (but this is not needed if the policy is 'noeviction').
 #
-# maxmemory <bytes>
+maxmemory {{ redis_maxmemory_bytes }}
 
 # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
 # is reached. You can select one from the following behaviors: