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Overview

Nested SPIRE allows SPIRE Servers to be “chained” together, and for all SPIRE Servers to issue identities in the same trust domain, meaning all workloads identified in the same trust domain are issued identity documents that can be verified against the root keys of the trust domain.

Nested topologies work by co-locating a SPIRE Agent with every downstream SPIRE Server being “chained”. The downstream SPIRE Server obtains credentials over the Workload API that it uses to directly authenticate with the upstream SPIRE Server to obtain an intermediate CA.

To demonstrate a deployment of SPIRE in a nested topology we create a scenario using Docker Compose with a root SPIRE deployment and two SPIRE deployments nested to it.

Nested SPIRE diagram

The nested topology is well suited for multi-cloud deployments. Due to the ability to mix and match node attestors, the downstream SPIRE Servers can reside and provide identities for workloads and SPIRE Agents in different cloud provider environments.

In this tutorial you will learn how to:

  • Configure SPIRE in a nested topology
  • Configure the UpstreamAuthority plugin
  • Create registration entries for nested SPIRE Servers
  • Test that SVIDs created in a nested configuration are valid in the entire trust domain

Prerequisites

Required files for this tutorial can be found in the nested-spire directory in https://github.com/spiffe/spire-tutorials. If you didn't already clone the repository please do so now.

Before proceeding, review the following system requirements:

  • A 64-bit Linux or macOS environment
  • Docker and Docker Compose installed (Docker Compose is included in macOS Docker Desktop)
  • Go 1.14.4 or higher installed

Part 1: Run Services

This tutorial's nested-spire main directory contains three subdirectories, one for each of the SPIRE deployments: root, nestedA and nestedB. These directories hold the configuration files for the SPIRE Servers and Agents. They will also contain the private keys and certificates created to attest the Agents on the Servers with the x509pop Node Attestor plugin. Private keys and certificates are created at the initialization of the scenario using a Go application, the details of which are out of the scope of this tutorial.

Create a Shared Directory

The first thing to do is to create a local directory that will be volume mounted on the services to share the Workload API between the root SPIRE Agent and its nested SPIRE Servers.

Ensure that the current working directory is .../spire-tutorials and change to the directory nested-spire that contains the required files to complete the tutorial:

    cd nested-spire

Create the sharedRootSocket shared directory:

   mkdir sharedRootSocket

Configuring Root SPIRE Deployment

Configuration files for root-server and root-agent have not been changed from the default server.conf and agent.conf files, but it's worth noting the location defined to bind the workload API socket by the SPIRE Agent: socket_path ="/opt/spire/sockets/workload_api.sock". This path will be used later to configure a volume to share the Workload API with the nested SPIRE Servers.

We define all the services for the tutorial in the docker-compose.yaml file. In the root-agent service definition we mount the /opt/spire/sockets directory from the SPIRE Agent container on the new local directory sharedRootSocket. In the next section, when defining the nested SPIRE Server services, we'll use this directory to mount the root-agent socket on the SPIRE Server containers.

   services:
     # Root
     root-server:
       image: gcr.io/spiffe-io/spire-server:0.10.1
       hostname: root-server
       volumes:
         - ./root/server:/opt/spire/conf/server
       command: ["-config", "/opt/spire/conf/server/server.conf"]
     root-agent:
       # Share the host pid namespace so this agent can attest the nested servers
       pid: "host"
       image: gcr.io/spiffe-io/spire-agent:0.10.1
       depends_on: ["root-server"]
       hostname: root-agent
       volumes:
         # Share root agent socket to be accessed by nestedA and nestedB servers
         - ./sharedRootSocket:/opt/spire/sockets
         - ./root/agent:/opt/spire/conf/agent
         - /var/run/:/var/run/
       command: ["-config", "/opt/spire/conf/agent/agent.conf"]

Configuring NestedA SPIRE Deployment

The same set of configurations are required for the nestedB SPIRE deployment but those changes are not described in the text to avoid needless repetition.

SPIRE Agent and Server can be extended with a variety of plugins. The UpstreamAuthority plugin type allows SPIRE Server to integrate with existing PKI systems. UpstreamAuthority plugins can sign certificates using CAs loaded from disk, third-party tools from AWS and Vault, and so on. Nested SPIRE deployments require the use of the spire UpstreamAuthority plugin which uses an upstream SPIRE Server in the same trust domain to obtain intermediate signing certificates for SPIRE Server.

The configuration file for the nestedA-server includes the spire UpstreamAuthority plugin definition with the root-server as its upstream SPIRE Server.

   UpstreamAuthority "spire" {
 	   plugin_data = {
 	       server_address      = "root-server"
 	       server_port         = 8081
 	       workload_api_socket = "/opt/spire/sockets/workload_api.sock"
 	   }
    }

The Docker Compose definition for the nestedA-server service in the docker-compose.yaml file mounts the new local directory sharedRootSocket as a volume. Remember from the previous section that the root-agent socket is mounted on that directory. That way the nestedA-server can access the root-agent workload API and fetch its SVID.

   nestedA-server:
     # Share the host pid namespace so this server can be attested by the root agent
     pid: "host"
     image: gcr.io/spiffe-io/spire-server:0.10.1
     hostname: nestedA-server
     labels:
       # label to attest nestedA-server against root-agent
       - org.example.name=nestedA
     volumes:
       # Add root agent socket  
       - ./shared/rootSocket:/opt/spire/sockets
       - ./nestedA/server:/opt/spire/conf/server
     command: ["-config", "/opt/spire/conf/server/server.conf"]

Create Downstream Registration Entry

The nestedA-server must be registered on the root-server to obtain its identity which will be used to mint SVIDs. We achieve this by creating a registration entry in the root SPIRE Server for the nestedA-server.

   docker-compose exec -T root-server \
       /opt/spire/bin/spire-server entry create \
       -parentID "spiffe://example.org/spire/agent/x509pop/$(fingerprint root/agent/agent.crt.pem)" \
       -spiffeID "spiffe://example.org/nestedA" \
       -selector "docker:label:org.example.name:nestedA-server" \
       -downstream \
       -ttl 3600

The -parentID flag contains the SPIFFE ID of the root-agent. The SPIFFE ID of the root-agent is created by the x509pop Node Attestor plugin which defines the SPIFFE ID as spiffe://<trust domain>/spire/agent/x509pop/<fingerprint>. A fingerprint() function in the shell script calculates the SHA1 fingerprint of the certificate. The other point to highlight is the -downstream option. This option, when set, indicates that the entry describes a downstream SPIRE Server.

Run the Scenario

Use the set-env.sh script to run all the services that make up the scenario. The script starts the root, nestedA, and nestedB services with the configuration options described earlier.

Ensure that the current working directory is .../spire-tutorials/nested-spire and run:

    bash scripts/set-env.sh

Once the script is completed, in another terminal run the following command to review the logs from all the services:

    docker-compose logs -f -t

Part 2: Test the Deployments

Now that the SPIRE deployments are ready, let's test the scenario that we've configured.

Create Workload Registration Entries

To test the scenario we create two workload registration entries, one entry for each nested SPIRE Server (nestedA and nestedB). The goal of the test is to demonstrate that SVIDs created in a nested configuration are valid in the entire trust domain, not only in the scope of the SPIRE Server that originated the SVID. The following commands demonstrate the command line options we'll use to create the two workload registration entries, but you can run these commands using the create-workload-registration-entries.sh script shown a few lines below.

   # Workload for nestedA deployment
   docker-compose exec -T nestedA-server \
       /opt/spire/bin/spire-server entry create \
       -parentID "spiffe://example.org/spire/agent/x509pop/$(fingerprint nestedA/agent/agent.crt.pem)" \
       -spiffeID "spiffe://example.org/nestedA/workload" \
       -selector "unix:uid:1001" \
       -ttl 0

   # Workload for nestedB deployment
   docker-compose exec -T nestedB-server \
       /opt/spire/bin/spire-server entry create \
       -parentID "spiffe://example.org/spire/agent/x509pop/$(fingerprint nestedB/agent/agent.crt.pem)" \
       -spiffeID "spiffe://example.org/nestedB/workload" \
       -selector "unix:uid:1001" \
       -ttl 0

The examples use the fingerprint path/to/nested-agent-cert form again to show that the -parentID flag specifies the SPIFFE ID of the nested SPIRE Agent. The TTL flag value of zero indicates that the default value of 3600 seconds will be used. Finally, in both cases the unix selector assigns the SPIFFE ID to any process with a uid of 1001.

Use the following Bash script to create the registration entries using the options just described:

   bash scripts/create-workload-registration-entries.sh

Run the Test

Once both workload registration entries are propagated, let's test that SVIDs created in a nested configuration are valid in the entire trust domain, not only in the scope of the SPIRE Server that originated the SVID.

The test consists of getting a JWT-SVID from the nestedA-agent SPIRE Agent and validating it using the nestedB-agent. In both cases, Docker Compose runs the processes using the uid 1001 to match the workload registration entries created in the previous section.

Type this command to fetch the JWT-SVID on the nestedA SPIRE Agent and extract the token from the JWT-SVID:

    token=$(docker-compose exec -u 1001 -T nestedA-agent \
      /opt/spire/bin/spire-agent api fetch jwt -audience nested-test -socketPath /opt/spire/sockets/workload_api.sock | sed -n '2p')

Run the following command to validate the token from nestedA on the nestedB SPIRE Agent:

    docker-compose exec -u 1001 -T nestedB-agent \
        /opt/spire/bin/spire-agent api validate jwt -audience nested-test  -svid "${token}" \
          -socketPath /opt/spire/sockets/workload_api.sock

The nestedB SPIRE Agent outputs the following:

    SVID is valid.
    SPIFFE ID : spiffe://example.org/nestedA/workload
    Claims    : {"aud":["nested-test"],"exp":1595814190,"iat":1595813890,"sub":"spiffe://example.org/nestedA/workload"}

The output indicates that the JWT-SVID is valid. Also, although the SPIFFE ID is registered on nestedA rather than nestedB, the SPIFFE ID is still valid on the nestedB SPIRE Agent because the SPIRE Agents are in the same trust domain in the nested SPIRE topology.

In SPIRE this is accomplished by propagating every JWT-SVID public signing key to the whole topology. In the case of X509-SVID, this is easily achieved because of the chaining semantics that X.509 has.

Cleanup

When you are finished running this tutorial, you can use the following Bash script to stop all the containers:

    bash scripts/clean-env.sh