Added 'subnetGroup' option

README.md

@@ -112,6 +112,12 @@ custom:
     services:
       - kms
       - secretsmanager
+
+    # optional
+    # can pick one of subnet groups in (rds / redshift / elasticache / dax)
+    # ex) DAX is not available in ap-northeast-2 so I don't want to make DAX subnet group
+    subnetGroup:
+      - rds
 ```
 
 ## CloudFormation Outputs

src/index.js

@@ -38,6 +38,7 @@ class ServerlessVpcPlugin {
     let createNatInstance = false;
     let createBastionHost = false;
     let bastionHostKeyName = null;
+    let subnetGroup = [];
 
     const { vpcConfig } = this.serverless.service.custom;
 
@@ -70,6 +71,9 @@ class ServerlessVpcPlugin {
       if (Array.isArray(vpcConfig.services)) {
         services = vpcConfig.services.map(s => s.trim().toLowerCase());
       }
+      if (Array.isArray(vpcConfig.subnetGroup) && vpcConfig.subnetGroup.length > 0) {
+        ({ subnetGroup } = vpcConfig);
+      }
 
       if ('createDbSubnet' in vpcConfig && typeof vpcConfig.createDbSubnet === 'boolean') {
         ({ createDbSubnet } = vpcConfig);
@@ -221,6 +225,8 @@ class ServerlessVpcPlugin {
     if (createDbSubnet) {
       if (numZones < 2) {
         this.serverless.cli.log('WARNING: less than 2 AZs; skipping subnet group provisioning');
+      } else if (subnetGroup.length > 0) {
+        Object.assign(resources, buildSubnetGroups(numZones, subnetGroup));
       } else {
         Object.assign(resources, buildSubnetGroups(numZones));
       }

src/subnet_groups.js

@@ -135,10 +135,22 @@ function buildDAXSubnetGroup(numZones = 0, { name = 'DAXSubnetGroup' } = {}) {
  * @param {Number} numZones Number of availability zones
  * @return {Object}
  */
-function buildSubnetGroups(numZones = 0) {
+function buildSubnetGroups(numZones = 0, subnetGroup = []) {
   if (numZones < 2) {
     return {};
   }
+  const subnetGroups = {
+    rds: buildRDSSubnetGroup,
+    redshift: buildRedshiftSubnetGroup,
+    elasticache: buildElastiCacheSubnetGroup,
+    dax: buildDAXSubnetGroup,
+  }
+  if (subnetGroup.length > 0) {
+    return subnetGroup.reduce(function(acc, service) {
+      let builtSubnetGroup = subnetGroups[service.toLowerCase()](numZones);
+      return Object.assign(acc, builtSubnetGroup);
+    }, {});
+  }
   return Object.assign(
     {},
     buildRDSSubnetGroup(numZones),