feat: introduce pgbouncer as a PostgreSQL proxy

anvil-python/anvil/versions.py

@@ -15,14 +15,16 @@
 
 MAAS_REGION_CHANNEL = "latest/edge"
 MAAS_AGENT_CHANNEL = "latest/edge"
-POSTGRESQL_CHANNEL = "14/stable"
+POSTGRESQL_CHANNEL = "14/candidate"
+PGBOUNCER_CHANNEL = "1/candidate"
 HAPROXY_CHANNEL = "latest/stable"
 
 MACHINE_CHARMS = {
     "maas-region": MAAS_REGION_CHANNEL,
     "maas-agent": MAAS_AGENT_CHANNEL,
     "haproxy": HAPROXY_CHANNEL,
     "postgresql": POSTGRESQL_CHANNEL,
+    "pgbouncer": PGBOUNCER_CHANNEL,
 }
 K8S_CHARMS: dict[str, str] = {}
 
@@ -43,7 +45,12 @@
             "channel": "charm_maas_region_channel",
             "revision": "charm_maas_region_revision",
             "config": "charm_maas_region_config",
-        }
+        },
+        "pgbouncer": {
+            "channel": "charm_pgbouncer_channel",
+            "revision": "charm_pgbouncer_revision",
+            "config": "charm_pgbouncer_config",
+        },
     }
 }
 

cloud/etc/deploy-maas-agent/main.tf

@@ -45,7 +45,7 @@ resource "juju_application" "maas-agent" {
   config = var.charm_maas_agent_config
 }
 
-resource "juju_integration" "maas-region-postgresql" {
+resource "juju_integration" "maas-agent-region" {
   model = data.juju_model.machine_model.name
 
   application {

cloud/etc/deploy-maas-region/main.tf

@@ -45,7 +45,39 @@ resource "juju_application" "maas-region" {
   config = var.charm_maas_region_config
 }
 
-resource "juju_integration" "maas-region-postgresql" {
+resource "juju_application" "pgbouncer" {
+  name  = "pgbouncer"
+  model = data.juju_model.machine_model.name
+  units = 0 # it is a subordinate charm
+
+  charm {
+    name     = "pgbouncer"
+    channel  = var.charm_pgbouncer_channel
+    revision = var.charm_pgbouncer_revision
+    base     = "ubuntu@22.04"
+  }
+
+  config = merge({
+    pool_mode          = "transaction"
+    max_db_connections = floor(90 / max(length(var.machine_ids), 1))
+  }, var.charm_pgbouncer_config)
+}
+
+resource "juju_integration" "postgresql-pgbouncer" {
+  model = data.juju_model.machine_model.name
+
+  application {
+    name     = "postgresql"
+    endpoint = "database"
+  }
+
+  application {
+    name     = juju_application.pgbouncer.name
+    endpoint = "backend-database"
+  }
+}
+
+resource "juju_integration" "maas-region-pgbouncer" {
   model = data.juju_model.machine_model.name
 
   application {
@@ -54,7 +86,7 @@ resource "juju_integration" "maas-region-postgresql" {
   }
 
   application {
-    name     = "postgresql"
+    name     = juju_application.pgbouncer.name
     endpoint = "database"
   }
 }

cloud/etc/deploy-maas-region/variables.tf

@@ -47,3 +47,21 @@ variable "enable_haproxy" {
   type        = bool
   default     = false
 }
+
+variable "charm_pgbouncer_channel" {
+  description = "Operator channel for PgBouncer deployment"
+  type        = string
+  default     = "1/candidate"
+}
+
+variable "charm_pgbouncer_revision" {
+  description = "Operator channel revision for PgBouncer deployment"
+  type        = number
+  default     = null
+}
+
+variable "charm_pgbouncer_config" {
+  description = "Operator config for PgBouncer deployment"
+  type        = map(string)
+  default     = {}
+}