bringing down the API

.github/workflows/terraform.yml

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+name: Terraform validation
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  terraform:
+    name: Terraform format and validate
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: terraform
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Terraform
+        uses: hashicorp/setup-terraform@v3
+
+      - name: Terraform Format
+        run: terraform fmt -check -recursive
+
+      - name: Terraform Init
+        run: terraform init -backend=false
+
+      - name: Terraform Validate
+        run: terraform validate

IPv6_MIGRATION_NOTES.md

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+# IPv6 Migration Attempt and Module Upgrade Notes
+
+## Executive Summary
+
+**Attempted:** IPv6-only EC2 instances to save ~$7-14/month on public IPv4 charges
+**Result:** **REVERTED** - Not viable without AWS NAT64 support
+**Successful:** Module version upgrades (ASG, Security Group, AWS Provider)
+
+## What We Tried (October 2025)
+
+### 1. IPv6-Only Configuration Attempt
+
+**Modified:** `terraform/asg.tf`
+- Disabled public IPv4: `associate_public_ip_address = false`
+- Enabled IPv6: `ipv6_address_count = 1`
+- Configured ECS agent and Docker for IPv6
+
+**Infrastructure verified working:**
+- ✅ VPC has IPv6 CIDR: `2600:1f16:78e:d400::/56`
+- ✅ Subnets have IPv6 CIDRs with auto-assign enabled
+- ✅ Route table: `::/0` → Internet Gateway
+- ✅ DNS64 enabled on all subnets
+- ✅ AWS dual-stack endpoints available:
+  - `ecs.us-east-2.api.aws` → `2600:1f70:6000:c0:...`
+  - `ecr.us-east-2.api.aws` → `2600:1f70:6000:80:...`
+  - `logs.us-east-2.api.aws` → `2600:1f70:6000:200:...`
+
+### Why It Failed
+
+**Root cause:** NAT64 requires NAT Gateway, which negates cost savings
+
+**What this means:**
+- **DNS64** (✅ provided): Translates DNS queries from A records to AAAA records using `64:ff9b::/96` prefix
+- **NAT64** (✅ available via NAT Gateway): AWS NAT Gateway supports NAT64 translation when routing `64:ff9b::/96` traffic through it
+- **The problem**: NAT Gateway costs ~$32+/month base, which exceeds the ~$18/month we'd save on public IPv4 addresses
+- Additionally, SSM still requires IPv4 connectivity regardless of NAT64
+
+**Services that broke:**
+- ❌ AWS SSM Agent (IPv4-only): `dial tcp [64:ff9b::392:b12]:443: i/o timeout`
+- ❌ ECS container health checks failed
+- ❌ Any IPv4-only external dependencies
+
+**Services that worked:**
+- ✅ ECS control plane (has dual-stack endpoint)
+- ✅ ECR (has dual-stack endpoint)
+- ✅ CloudWatch Logs (has dual-stack endpoint)
+
+### 2. Terraform Module Version Upgrades (SUCCESSFUL)
+
+**Successfully Updated Modules:**
+
+| Module | Old Version | New Version | Status |
+|--------|-------------|-------------|--------|
+| `terraform-aws-modules/autoscaling/aws` | ~> 6.5 | ~> 8.3 | ✅ Applied |
+| `terraform-aws-modules/security-group/aws` | ~> 4.0 | ~> 5.3 | ✅ Applied |
+| AWS Provider | >= 4.6 | >= 5.0 | ✅ Applied |
+| `terraform-aws-modules/ecs/aws` | ~> 4.0 | ~> 4.1 | ✅ Applied (kept at v4 to avoid cluster recreation) |
+
+**Why we didn't go further:**
+- ECS v6.x: Breaking API changes (cluster recreation required)
+- ASG v9.x: Breaking changes in `mixed_instances_policy` structure
+
+**Installed Versions:**
+- AWS Provider: v5.100.0
+- ECS Module: v4.1.3
+- Autoscaling Module: v8.3.1
+- Security Group Module: v5.3.1
+
+## Current Configuration (Post-Revert)
+
+**Final State:**
+- ✅ Instances have public IPv4 (reverted from IPv6-only)
+- ✅ Instances have IPv6 addresses
+- ✅ Dual-stack networking
+- ✅ Module upgrades applied
+- ❌ No cost savings (still paying for public IPv4)
+
+**Configuration:**
+```hcl
+# terraform/asg.tf
+network_interfaces = [
+  {
+    associate_public_ip_address = true   # Reverted to true
+    ipv6_address_count          = 1      # Still have IPv6
+    # ...
+  }
+]
+
+# terraform/ecs.tf - user_data
+# Standard ECS config, no IPv6-specific settings
+```
+
+## What Would Need to Change for IPv6-Only to Work
+
+**Waiting for AWS to provide:**
+
+1. **SSM dual-stack endpoints** (main blocker)
+   - SSM, EC2 Messages, and SSM Messages currently require IPv4
+   - Without this, managed EC2 instances cannot go IPv6-only
+   - NAT64 via NAT Gateway exists but costs ~$32+/month (negates savings)
+
+2. **Alternative: All management services support dual-stack**
+   - Particularly: SSM, EC2 Messages, SSM Messages
+   - Currently ECS, ECR, CloudWatch Logs, S3, IAM support dual-stack
+
+**Self-managed workarounds we rejected:**
+
+1. **Deploy NAT64 on EC2** (Jool/Tayga software)
+   - Cost: ~$3-5/month + maintenance burden
+   - Complexity: High (setup, monitoring, SPOF)
+   - Not worth $7-14/month savings
+
+2. **VPC Endpoints for IPv4-only services**
+   - Cost: ~$7-10/month
+   - Would eliminate savings
+   - Previous testing showed higher cost than benefit
+
+3. **Disable SSM entirely**
+   - Lose remote management capability
+   - Not acceptable for production
+
+## Lessons Learned
+
+### What We Discovered
+
+1. **DNS64 ≠ NAT64**
+   - DNS64 only translates DNS queries, not actual traffic
+   - Need both DNS64 + NAT64 for IPv6-only to work
+   - AWS provides DNS64 but not NAT64
+
+2. **Docker IPv6 Configuration Issues**
+   - Enabling Docker IPv6 (`"ipv6": true`) broke dual-stack networking
+   - Caused container health check failures
+   - Required instance refresh to fix
+
+3. **AWS Service IPv6 Support is Inconsistent**
+   - Some services have dual-stack: ECS, ECR, CloudWatch, S3
+   - Some services are IPv4-only: SSM, EC2 Messages
+   - Use `.api.aws` suffix for dual-stack endpoints when available
+
+4. **Cost-Benefit Analysis**
+   - Potential savings: ~$7-14/month (public IPv4 charges)
+   - VPC endpoint costs: ~$7-10/month (negates savings)
+   - Self-managed NAT64: High complexity for minimal savings
+   - **Conclusion:** Not worth the effort at this scale
+
+### Technical Details Documented
+
+**VPC IPv6 Configuration:**
+- VPC CIDR: `2600:1f16:78e:d400::/56`
+- Subnets: `2600:1f16:78e:d400::/64`, `d401::/64`, `d402::/64`
+- DNS64 prefix: `64:ff9b::/96`
+- Route: `::/0` → `igw-e39ab08a`
+
+**Error signatures to watch for:**
+```
+dial tcp [64:ff9b::xxx:xxx]:443: i/o timeout
+```
+This indicates DNS64 translation without NAT64 gateway.
+
+## Future Retry Conditions
+
+**Only attempt IPv6-only again when ONE of these is true:**
+
+1. ✅ **SSM gets dual-stack endpoints**
+   - Specifically need: SSM, EC2 Messages, SSM Messages with IPv6
+   - This is the primary blocker for managed EC2 instances
+   - Check: https://docs.aws.amazon.com/vpc/latest/userguide/aws-ipv6-support.html
+
+2. ✅ **NAT Gateway pricing drops significantly**
+   - Currently ~$32+/month base cost negates IPv4 savings
+   - Would need to be <$10/month to make economic sense
+
+3. ✅ **Public IPv4 costs exceed $20-30/month**
+   - At current scale (2-4 instances), savings too small
+   - If scale increases significantly, complexity might be worth it
+
+4. ✅ **VPC Endpoint costs drop significantly**
+   - If AWS reduces endpoint pricing below ~$3/month per endpoint
+   - Would make endpoint solution viable
+
+**How to check service IPv6 support:**
+```bash
+dig service-name.region.api.aws AAAA +short
+# If returns IPv6 address, service supports dual-stack
+```
+
+**Track AWS IPv6 progress:**
+- Official tracker: https://docs.aws.amazon.com/vpc/latest/userguide/aws-ipv6-support.html
+- AWS What's New (filter for IPv6): https://aws.amazon.com/new/
+
+**Key services to watch for IPv6-only viability:**
+- SSM (Systems Manager) - currently IPv4-only, this is the main blocker
+- EC2 Messages - currently IPv4-only
+- SSM Messages - currently IPv4-only
+
+**Last checked:** January 2026 - SSM still requires IPv4 connectivity
+
+## Rollback Summary
+
+**What we reverted:**
+1. Changed `associate_public_ip_address` back to `true`
+2. Removed IPv6-specific ECS agent configuration
+3. Removed Docker IPv6 configuration
+4. Triggered instance refresh to replace broken instances
+
+**What we kept:**
+- IPv6 addressing (instances have both IPv4 and IPv6)
+- Module version upgrades
+- Updated security group module
+
+**Recovery time:** ~5 minutes for instance refresh to complete