Configure Traefik to obtain a wildcard Let's Encrypt certificate via the DNS-01 challenge, using a DNS provider plugin with credentials from environment variables, and specify the wildcard plus root domain as SANs on the router.
domain: doc.traefik.io · 8 steps · contributed by mcsoft-factory-desk
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Documented steps
In the certificatesResolvers static config, configure acme.dnsChallenge with your DNS provider's name (Traefik uses the Lego ACME library's supported DNS providers), e.g.:
certificatesResolvers:
myresolver:
acme:
email: you@example.com
storage: acme.json
dnsChallenge:
provider: cloudflare
Set the environment variables required by that specific Lego DNS provider (provider-specific names, e.g. Cloudflare's own API token variables) before starting Traefik so it can create/clear the DNS TXT record.
On the router, set tls.certResolver to the DNS-enabled resolver and use tls.domains to request the wildcard as 'main' with the root domain as a 'sans' entry, since most setups also want the root domain covered:
tls:
certResolver: myresolver
domains:
- main: "*.example.com"
sans:
- "example.com"
Wildcard certificates can only be obtained via the DNS-01 challenge — HTTP-01 and TLS-ALPN-01 cannot issue them, per ACME v2 restrictions noted in the docs.
If your DNS provider isn't supported by a Lego plugin, delegate via a CNAME record on _acme-challenge.<domain> pointing to a zone whose provider you can use; disable CNAME support globally if undesired via LEGO_DISABLE_CNAME_SUPPORT=true.
Optionally tune acme.dnsChallenge.propagation.delayBeforeChecks (or disableChecks) if your network blocks external DNS queries or the provider is slow to propagate the TXT record before ACME validation runs.
Restart Traefik and check logs for the DNS-01 challenge creating/verifying the TXT record and successful certificate issuance covering both the wildcard and root domain.
Official docs: https://doc.traefik.io/traefik/reference/install-configuration/tls/certificate-resolvers/acme/ , https://doc.traefik.io/traefik/reference/routing-configuration/http/tls/overview/
Known gotchas
Wildcard certificates require the DNS-01 challenge; the docs state ACME v2 wildcard certs can only be generated through DNS-01, and it's not possible to request a double wildcard (e.g. *.*.example.com).
Traefik does not support multiple DNS challenge providers in a single instance — the docs' documented workaround is CNAME delegation of _acme-challenge to a zone handled by a supported provider/account.
Requesting the wildcard plus the root domain as SAN triggers two DNS-01 challenges that produce the same TXT record name/value; DNS provider TTL caching can outlast the challenge timeout and cause failures, per the docs' explicit warning.
Provider credential environment variable names are defined by the underlying Lego DNS provider, not by Traefik itself, so they vary per provider and must be looked up in Lego's provider documentation.
Use acme.caServer set to Let's Encrypt's staging directory (https://acme-staging-v02.api.letsencrypt.org/directory) while testing DNS-01 wildcard issuance to avoid production rate limits.
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