Securing Sensu

As with any piece of software, it is critical to minimize any attack surface exposed by the software. Sensu is no different. The following component pieces need to be secured in order for Sensu to be considered production ready:

We’ll cover securing each one of those pieces, starting with etcd peer communication.

Securing etcd peer communication

While enabling secure agent-to-server communication involves the change of one line, securing etcd peer communication is more involved and requires modifying several attributes inside of the configuration at /etc/sensu/backend.yml. Let’s look at the parameters you’ll need to configure:

##
# backend store configuration
##
etcd-listen-client-urls: "https://localhost:2379"
etcd-listen-peer-urls: "https://localhost:2380"
etcd-initial-advertise-peer-urls: "https://localhost:2380"
etcd-cert-file: "/path/to/your/cert"
etcd-key-file: "/path/to/your/key"
etcd-trusted-ca-file: "/path/to/your/ca/file"
etcd-peer-cert-file: "/path/to/your/peer/cert"
etcd-peer-key-file: "/path/to/your/peer/key"
etcd-peer-client-cert-auth: "true"
etcd-peer-trusted-ca-file: "/path/to/your/peer/ca/file"

Securing the API and the dashboard

Both the Sensu Go API and the dashboard use a common stanza in /etc/sensu/backend.yml to provide the certificate, key, and CA file needed to provide secure communication. Let’s look at the attributes you’ll need to configure:

##
# backend ssl configuration
##
cert-file: "/path/to/ssl/cert.pem"
key-file: "/path/to/ssl/key.pem"
trusted-ca-file: "/path/to/trusted-certificate-authorities.pem"
insecure-skip-tls-verify: false

Providing the above cert-file and key-file parameters will cause the API to serve HTTP requests over SSL/TLS (https). As a result, you will also need to specify https:// schema for the api-url parameter:

##
# backend api configuration
##
api-url: "https://localhost:8080"

In the example above, we provide the path to the cert, key and CA file. After restarting the sensu-backend service, the parameters are loaded and you are able to access the dashboard at https://localhost:3000. Configuring these attributes will also ensure that agents are able to communicate securely. Let’s move on to securing agent to server communication.

Securing Sensu agent to server communication

The Sensu agent uses WebSockets for communication between the agent and the server. By default, an agent uses the insecure ws:// transport. Let’s look at the example from /etc/sensu/agent.yml:

---
##
# agent configuration
##
backend-url:
  - "ws://127.0.0.1:8081"

In order to use WebSockets over SSL/TLS (wss), change the backend-url value to the wss:// schema:

---
##
# agent configuration
##
backend-url:
  - "wss://127.0.0.1:8081"

The agent will then connect Sensu servers over wss. Do note that by changing the configuration to wss, plaintext communication will not be possible.

NOTE: If creating a Sensu cluster, every cluster member needs to be present in the configuration. See the Sensu Go clustering guide for more information on how to configure agents for a clustered configuration.

Hopefully you’ve found this useful! If you find any issues or have any questions, feel free to reach out in our Community Slack, or open an issue on Github.