Confusing error condition configuring tls

Traefik Traefik v3 (latest)
,
1

i’m configuring traefik in a stripped-down ubuntu docker container with a USERTrust cert with a complete chain in a PEM file.

My cert passes inspection with openssl
My key file does as well

The paths are listed correctly in traefik.toml under [[tls.certificates]].
When I enter the running container, I find the cert and key files in /etc/traefik/certs/
They have correct permissions and i can cat them.

When i start traefik, I get the following errors:

traefik-1 | 2025-11-06T01:04:35Z ERR ``github.com/traefik/traefik/v3/pkg/tls/tlsmanager.go:137`` > Unable to parse certificate /etc/traefik/certs/mycert error="unable to generate TLS certificate: tls: failed to find any PEM data in certificate input" traefik-1 | 2025-11-06T01:04:35Z ERR ``github.com/traefik/traefik/v3/pkg/tls/tlsmanager.go:194`` > Error while creating certificate store error="failed to load X509 key pair: tls: failed to find any PEM data in certificate input" tlsStoreName=default

==> I get the same error when I list a non-existent file in traefik.toml

How can I get more information about why traefik isn’t able to find and/or read the certFile ??

/ # traefik version
Version: 3.5.3
Codename: chabichou
Go version: go1.24.7
Built: 2025-09-26T09:20:06Z
OS/Arch: linux/amd64

Thanks,

-Rob

2

Your cert file looks like this when you cat it?

-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
3

It does. And openssl decodes it as expected and it loads correctly in an nginx environment.

The problem isn’t the cert, it’s traefik’s inability or failure to read the cert file.

4

Works for me with Traefik v3.5.3:

tls:
  options:
    default:
      minVersion: VersionTLS12
  certificates:
    - certFile: /config/example.com.crt
      keyFile: /config/example.com.key

Example TLS cert generated with LetsEncrypt via acme.sh.