AWS Bedrock Error: Bedrock Invocation Fails from Private Subnet
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A diagnostic guide to resolving AWS Bedrock invocation failures caused by missing outbound network access from private VPC subnets.
Problem
An AWS Bedrock invocation fails when the workload runs in a private subnet.
Typical symptoms:
- The same code works locally or in a public subnet
- IAM permissions and model access are correct
- Requests time out or fail without a clear Bedrock error
- Retries do not help
- Inference never begins.
Clarifying the Issue
This is not an IAM problem and not a Bedrock service outage.
It occurs when a workload running in a private subnet has no network path to reach the Bedrock service.
AWS Bedrock is a regional AWS-managed service.
Workloads in private subnets must have one of the following:
- Explicit outbound egress (NAT Gateway), or
- A private connection (VPC Endpoint / PrivateLink)
Without one of these, the request never reaches Bedrock.
Why It Matters
This failure commonly appears when:
- Lambda functions are attached to a VPC
- ECS tasks or EC2 instances run in private subnets
- NAT gateways are removed for cost or security reasons
- Architects expect private services to be reachable automatically
Engineers often debug IAM or SDKs when the issue is purely network reachability.
Key Terms
- Private subnet – A subnet without direct internet access
- NAT gateway – Enables outbound internet access from private subnets
- VPC endpoint (PrivateLink) – Private connectivity to AWS services without internet access
- Route table – Controls traffic flow for a subnet
Steps at a Glance
- Confirm the workload runs in a private subnet
- Check for outbound egress (NAT) or a VPC endpoint
- Verify route table configuration
- Validate security group egress rules
- Retest Bedrock invocation
Detailed Steps
1. Confirm the Subnet Type
Verify where the workload runs:
- Lambda → VPC configuration → Subnets
- ECS / EC2 → Subnet assignment
If the subnet has no route to an Internet Gateway, it is private.
2. Check for NAT Gateway or VPC Endpoint
You must have one of the following:
Option A: NAT Gateway (Fastest Fix)
- NAT gateway exists in a public subnet
- NAT gateway status is
Available
Option B: VPC Endpoint (Preferred for Enterprise)
- A VPC endpoint for Amazon Bedrock is configured
- Endpoint is associated with the private subnets
- Security groups allow HTTPS traffic to the endpoint
Either option is valid.
3. Verify the Route Table
For NAT-based access, confirm the private subnet route table includes:
0.0.0.0/0→nat-xxxxxxxx
For VPC endpoints, ensure:
- No conflicting routes block endpoint traffic
4. Validate Security Group Egress
Minimum requirement:
- Outbound: Allow TCP 443
Overly restrictive egress rules will block Bedrock traffic even if routing is correct.
5. Retest the Invocation
Retry the Bedrock call.
If invocation succeeds, the root cause was missing or misconfigured network access.
Pro Tips
- Attaching Lambda to a VPC removes default internet access
- Better Alternative: A VPC Endpoint (PrivateLink) avoids NAT costs and keeps traffic private
- NAT is a quick fix; endpoints are the long-term enterprise solution
- Bedrock does not run inside your VPC
Conclusion
When Bedrock invocation fails from a private subnet, the issue is network reachability, not permissions.
Once:
- The subnet has NAT egress or a VPC endpoint
- Route tables are correct
- Security groups allow outbound HTTPS
AWS Bedrock invocation works normally inside Amazon Web Services.
On a final note, confirm connectivity, then retry the call. Your Bedrock invocation should work now work successfully
Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.
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