See also [Let's Encrypt examples](/user-guide/examples/#lets-encrypt-support) and [Docker & Let's Encrypt user guide](/user-guide/docker-and-lets-encrypt).
**WARNING** If you use Traefik in Docker, you have 2 options:
- create a file on your host and mount it as a volume:
```toml
storage = "acme.json"
```
```bash
docker run -v "/my/host/acme.json:acme.json" traefik
```
- mount the folder containing the file as a volume
```toml
storage = "/etc/traefik/acme/acme.json"
```
```bash
docker run -v "/my/host/acme:/etc/traefik/acme" traefik
```
### `dnsProvider`
```toml
[acme]
# ...
dnsProvider = "digitalocean"
# ...
```
Use a DNS based acme challenge rather than external HTTPS access, e.g. for a firewalled server.
Select the provider that matches the DNS domain that will host the challenge TXT record, and provide environment variables with access keys to enable setting it:
By default, the dnsProvider will verify the TXT DNS challenge record before letting ACME verify.
If `delayDontCheckDNS` is greater than zero, avoid this & instead just wait so many seconds.
Useful if internal networks block external DNS queries.
### `onDemand`
```toml
[acme]
# ...
onDemand = true
# ...
```
Enable on demand certificate.
This will request a certificate from Let's Encrypt during the first TLS handshake for a hostname that does not yet have a certificate.
!!! warning
TLS handshakes will be slow when requesting a hostname certificate for the first time, this can leads to DoS attacks.
!!! warning
Take note that Let's Encrypt have [rate limiting](https://letsencrypt.org/docs/rate-limits)
### `onHostRule`
```toml
[acme]
# ...
onHostRule = true
# ...
```
Enable certificate generation on frontends Host rules.
This will request a certificate from Let's Encrypt for each frontend with a Host rule.
For example, a rule `Host:test1.traefik.io,test2.traefik.io` will request a certificate with main domain `test1.traefik.io` and SAN `test2.traefik.io`.
