From be1e7bd758e6ebc60fc161829a049480c8e71a25 Mon Sep 17 00:00:00 2001
From: Stan Rudenko <stan@truera.com>
Date: Fri, 18 Aug 2023 18:10:25 -0700
Subject: [PATCH] agent mode support

---
 roles/prometheus/defaults/main.yml               |  5 +++++
 roles/prometheus/meta/argument_specs.yml         | 10 ++++++++++
 roles/prometheus/templates/prometheus.service.j2 |  9 +++++++--
 roles/prometheus/templates/prometheus.yml.j2     |  2 ++
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/roles/prometheus/defaults/main.yml b/roles/prometheus/defaults/main.yml
index 72a85c7e6..930d9139f 100644
--- a/roles/prometheus/defaults/main.yml
+++ b/roles/prometheus/defaults/main.yml
@@ -25,6 +25,9 @@ prometheus_storage_retention: "30d"
 # supported: KB, MB, GB, TB, PB.
 prometheus_storage_retention_size: "0"
 
+# The Agent mode optimizes Prometheus for the remote write use case: https://prometheus.io/blog/2021/11/16/agent/
+prometheus_agent_mode: false
+
 prometheus_config_flags_extra: {}
 # prometheus_config_flags_extra:
 #   storage.tsdb.retention: 15d
@@ -87,6 +90,8 @@ prometheus_scrape_configs:
 # Alternative config file name, searched in ansible templates path.
 prometheus_config_file: 'prometheus.yml.j2'
 
+prometheus_rules_enable: true
+
 prometheus_alert_rules_files:
   - prometheus/rules/*.rules
 
diff --git a/roles/prometheus/meta/argument_specs.yml b/roles/prometheus/meta/argument_specs.yml
index 663afa30f..a791711e7 100644
--- a/roles/prometheus/meta/argument_specs.yml
+++ b/roles/prometheus/meta/argument_specs.yml
@@ -59,6 +59,12 @@ argument_specs:
           - "Maximum number of bytes that can be stored for blocks."
           - "Units supported: KB, MB, GB, TB, PB."
         default: "0"
+      prometheus_agent_mode:
+        description:
+          - "The Agent mode optimizes Prometheus for the remote write use case. It disables querying, alerting, and local storage, and replaces it with a customized TSDB WAL. L(Everything,https://prometheus.io/docs/prometheus/latest/feature_flags/#prometheus-agent) else stays the same."
+          - "This feature is available starting from Prometheus v2.32.0."
+        type: bool
+        default: false
       prometheus_config_flags_extra:
         description:
           - "Additional configuration flags passed to prometheus binary at startup"
@@ -121,6 +127,10 @@ argument_specs:
       prometheus_config_file:
         description: "Variable used to provide custom prometheus configuration file in form of ansible template"
         default: "prometheus.yml.j2"
+      prometheus_rules_enable:
+        description: "To enable rules via the rule_files field in the Prometheus configuration"
+        type: bool
+        default: true
       prometheus_alert_rules:
         description:
           - "Full list of alerting rules which will be copied to C({{ prometheus_config_dir }}/rules/ansible_managed.rules)."
diff --git a/roles/prometheus/templates/prometheus.service.j2 b/roles/prometheus/templates/prometheus.service.j2
index 7d2973af8..bbab7f8d7 100644
--- a/roles/prometheus/templates/prometheus.service.j2
+++ b/roles/prometheus/templates/prometheus.service.j2
@@ -13,12 +13,16 @@ User=prometheus
 Group=prometheus
 ExecReload=/bin/kill -HUP $MAINPID
 ExecStart={{ _prometheus_binary_install_dir }}/prometheus \
+{% if not prometheus_agent_mode %}
   --storage.tsdb.path={{ prometheus_db_dir }} \
-{% if prometheus_version is version('2.7.0', '>=') %}
+  {% if prometheus_version is version('2.7.0', '>=') %}
   --storage.tsdb.retention.time={{ prometheus_storage_retention }} \
   --storage.tsdb.retention.size={{ prometheus_storage_retention_size }} \
-{% else %}
+  {% else %}
   --storage.tsdb.retention={{ prometheus_storage_retention }} \
+  {% endif %}
+{% else %}
+  --enable-feature=agent \
 {% endif %}
 {% if prometheus_version is version('2.24.0', '>=') %}
   --web.config.file={{ prometheus_config_dir }}/web.yml \
@@ -54,6 +58,7 @@ RestrictSUIDSGID=true
 
 {% if (ansible_facts.packages.systemd | first).version is version('231', '>=') %}
 ReadWritePaths={{ prometheus_db_dir }}
+WorkingDirectory={{ prometheus_db_dir }}
 {% for path in prometheus_read_only_dirs %}
 ReadOnlyPaths={{ path }}
 {% endfor %}
diff --git a/roles/prometheus/templates/prometheus.yml.j2 b/roles/prometheus/templates/prometheus.yml.j2
index a6ed81284..97d6eea1e 100644
--- a/roles/prometheus/templates/prometheus.yml.j2
+++ b/roles/prometheus/templates/prometheus.yml.j2
@@ -17,8 +17,10 @@ remote_read:
   {{ prometheus_remote_read | to_nice_yaml(indent=2,sort_keys=False) | indent(2, False) }}
 {% endif %}
 
+{% if prometheus_rules_enable and not prometheus_agent_mode %}
 rule_files:
   - {{ prometheus_config_dir }}/rules/*.rules
+{% endif %}
 
 {% if prometheus_alertmanager_config | length > 0 %}
 alerting: