--- layout: docs page_title: Service Mesh Certificate Authority - AWS Certificate Manager description: >- You can use the AWS Certificate Manager Private Certificate Authority as the Consul service mesh's certificate authority to secure your service mesh. Learn how to configure the AWS ACM Private CA, its limitations in Consul, and cost planning considerations. --- # AWS Certificate Manager as a Service Mesh Certificate Authority Consul can be used with [AWS Certificate Manager (ACM) Private Certificate Authority (CA)](https://aws.amazon.com/certificate-manager/private-certificate-authority/) to manage and sign certificates. -> This page documents the specifics of the AWS ACM Private CA provider. Please read the [certificate management overview](/consul/docs/connect/ca) page first to understand how Consul manages certificates with configurable CA providers. ## Requirements The ACM Private CA Provider was added in Consul 1.7.0. The ACM Private CA Provider needs to be authorized via IAM credentials to perform operations. Every Consul server needs to be running in an environment where a suitable IAM configuration is present. The [standard AWS SDK credential locations](https://docs.aws.amazon.com/sdk-for-go/v1/developer-guide/configuring-sdk.html#specifying-credentials) are used, which means that suitable credentials and region configuration need to be present in one of the following: 1. Environment variables 1. Shared credentials file 1. Via an EC2 instance role The IAM credential provided must have permission for the following actions: - CreateCertificateAuthority - assuming an existing CA is not specified in `existing_arn` - DescribeCertificateAuthority - GetCertificate - IssueCertificate ## Configuration The ACM Private CA provider is enabled by setting the CA provider to `"aws-pca"` in the agent's [`ca_provider`] configuration option, or via the [`/connect/ca/configuration`] API endpoint. At this time there is only one, optional configuration value. Example configurations are shown below: ```hcl # ... connect { enabled = true ca_provider = "aws-pca" ca_config { existing_arn = "arn:aws:acm-pca:region:account:certificate-authority/12345678-1234-1234-123456789012" } } ``` ```json { "Provider": "aws-pca", "Config": { "ExistingARN": "arn:aws:acm-pca:region:account:certificate-authority/12345678-1234-1234-123456789012" } } ``` ~> **Note**: Suitable AWS IAM credentials are necessary for the provider to work. However, these are not configured in the Consul config which is typically on disk, and instead rely on the [standard AWS SDK configuration locations](https://docs.aws.amazon.com/sdk-for-go/v1/developer-guide/configuring-sdk.html#specifying-credentials). The configuration options are listed below. -> **Note**: The first key is the value used in API calls, and the second key (after the `/`) is used if you are adding the configuration to the agent's configuration file. - `ExistingARN` / `existing_arn` (`string: `) - The Amazon Resource Name (ARN) of an existing private CA in your ACM account. If specified, Consul will attempt to use the existing CA to issue certificates. - In the primary datacenter this ARN **must identify a root CA**. See [limitations](#limitations). - In a secondary datacenter, it must identify a subordinate CA signed by the same root used in the primary datacenter. If it is signed by another root, Consul will automatically create a new subordinate signed by the primary's root instead. The default behavior with no `ExistingARN` specified is for Consul to create a new root CA in the primary datacenter and a subordinate CA in each secondary DC. @include 'http_api_connect_ca_common_options.mdx' ## Limitations ACM Private CA has several [limits](https://docs.aws.amazon.com/acm-pca/latest/userguide/PcaLimits.html) that restrict how fast certificates can be issued. This may impact how quickly large clusters can rotate all issued certificates. Currently, the ACM Private CA provider for service mesh has some additional limitations described below. ### Unable to Cross-sign Other CAs It's not possible to cross-sign other CA provider's root certificates during a migration. ACM Private CA is capable of doing that through a different workflow but is not able to blindly cross-sign another root certificate without a CSR being generated. Both Consul's built-in CA and Vault can do this and the current workflow for managing CAs relies on it. For now, the limitation means that once ACM Private CA is configured as the CA provider, it is not possible to reconfigure a different CA provider, or rotate the root CA key without potentially observing some transient connection failures. See the section on [forced rotation without cross-signing](/consul/docs/connect/ca#forced-rotation-without-cross-signing) for more details. ### Primary DC Must be a Root CA Currently, if an existing ACM Private CA is used, the primary DC must use a Root CA directly to issue certificates. ## Cost Planning To help estimate costs, an example is provided below of the resources that would be used. ~> This is intended to illustrate the behavior of the CA for cost planning purposes. Please refer to the [pricing for ACM Private CA](https://aws.amazon.com/certificate-manager/pricing/) for actual cost information. Assume the following Consul datacenters exist and are configured to use ACM Private CA as their service mesh CA with the default leaf certificate lifetime of 72 hours: | Datacenter | Primary | CA Resource Created | Number of service instances | | ---------- | ------- | ------------------- | --------------------------- | | dc1 | yes | 1 ROOT | 100 | | dc2 | no | 1 SUBORDINATE | 50 | | dc3 | no | 1 SUBORDINATE | 500 | Leaf certificates are valid for 72 hours but are refreshed when between 60% and 90% of their lifetime has elapsed. On average each certificate will be reissued every 54 hours or roughly 13.3 times per month. So monthly cost would be calculated as: - 3 ⨉ Monthly CA cost, plus - 8630 ⨉ Certificate Issue cost, made up of: - 100 ⨉ 13.3 = 1,330 certificates issued in dc1 - 50 ⨉ 13.3 = 665 certificates issued in dc2 - 500 ⨉ 13.3 = 6,650 certificates issued in dc3 The number of certificates issued could be reduced by increasing [`leaf_cert_ttl`](/consul/docs/agent/config/config-files#ca_leaf_cert_ttl) in the CA Provider configuration if the longer lived credentials are an acceptable risk tradeoff against the cost. [`ca_config`]: /consul/docs/agent/config/config-files#connect_ca_config [`ca_provider`]: /consul/docs/agent/config/config-files#connect_ca_provider [`/connect/ca/configuration`]: /consul/api-docs/connect/ca#update-ca-configuration