When I want to add a Docker sensor to my PRTG server, PRTG asks me to provide a private key and a certificate to access my Docker instance. Where can I get these Docker credentials? How do I create a Docker certificate and private key?
This article applies to PRTG Network Monitor 15.4.22 or later
Generating Docker Certificate and Private Key for PRTG
If you add the Docker Container Status sensor (available as of PRTG version 15.4.22) to PRTG, you will need to provide a Private Key and a Certificate to request monitoring data from Docker. This approach ensures a secure connection to Docker from PRTG, authenticated by a certificate signed by a trusted certificate authority (CA).
So before you add the sensor, please create certificate and keys with OpenSSL. See this article for how to install OpenSSL (Step 1: Install Open SSL). Of course, if you already have Docker certificates available, you can use one of these.
Please find detailed instructions to create Docker certificates and keys in the Docker documentation:
Steps to Go
In general, you need to go through the following steps:
- Generate CA private and public keys using OpenSSL.
- Create server key and certificate signing request (CSR).
- Ensure the Common Name matches the hostname used to connect to Docker.
- Sign the public key with the CA.
- Configure the Docker daemon to accept connections from clients which provide a trusted certificate from your CA, for example:
$ dockerd -H tcp://0.0.0.0:2376 -H fd:// --tlsverify=true --tlscacert=ca.pem --tlscert=cert.pem --tlskey=key.pem $other_args
- -H tcp:0.0.0.0:2376 makes the Docker API available for all external IP addresses on port 2376. This is the port number you have to provide in section Docker Credentials of the sensor settings.
- -H fd:// makes the API locally available to get the Docker commands to work on the console.
- --tlsverify=true defines the access as SSL encrypted and that any connecting client has to authenticate.
- The certificates and keys (ending with .pem) are used for authentication of the sensor.
For more details like the exact commands and what you have to additionally consider, please see the Docker documentation.
Note: In older Docker versions the string to accept connections was:
$ docker daemon -H tcp://0.0.0.0:2376 -H fd:// --tlsverify=true --tlscacert=ca.pem --tlscert=cert.pem --tlskey=key.pem
Note: If you have any issues when creating certificates and keys for Docker, please contact Docker support!
Add the Sensor to PRTG
Now you have everything ready to monitor your Docker containers:
- In the Add Sensor dialog, enter the number of the Port you made available for API calls, usually port 2376.
- Open the file with the private key that you created before (for example, key.pem) with a text editor. Copy everything that this file contains and paste it into the Private Key field in the sensor settings.
- Open the server certificate file (for example, cert.pem) with a text editor. Copy everything that this file contains and paste it into the Certificate field in the sensor settings.
Done! Complete the Add Sensor dialog and PRTG starts to monitor the status of your desired Docker containers.
With the newer Docker versions ("dockerd" instead of "docker daemon") the string have to look like:
dockerd -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2376 --tlsverify=true --tlscacert=ca.pem --tlscert=cert.pem --tlskey=key.pem $other_args
Successfully tested with Docker 17.12 on CentOS 7 and PRTG 220.127.116.1128+. Configured in /etc/systemd/system/docker.service.d/source-sysconfig.conf
Thank you for the update, Mark! We added it to the article.
Forgive the perhaps dumb question, but can I also use a self-signed certificate? My docker-host is inside a private network without any connection to the big bad internet and therefore doesn't need a publicly recognized certificate...
As long as the CA that issues the certificate is trusted from the server where PRTG runs on, then you shouldn't run into any issues. Just make sure that the certificate and the root certificate from the CA are in the SYSTEM-Store of the PRTG Server.
Are there any plans to make docker monitoring easier to monitor?
Currently there are no plans to develop this sensor further and to offer more options, the main reason is that the usage-rate of this sensor is rather low.