If you set this environment variable value to `https://acme-staging-v02.api.letsencrypt.org/directory` the container will obtain its certificates from Let's Encrypt test API endpoint that don't have the [5 certs/week/domain limit](https://letsencrypt.org/docs/rate-limits/) (but are not trusted by browsers).
*`DEBUG` - Set it to `1` to enable debugging of the entrypoint script and generation of LetsEncrypt certificates, which could help you pin point any configuration issues.
*`RENEW_PRIVATE_KEYS` - Set it to `false` to make `acme.sh` reuse previously generated private key for each certificate instead of creating a new one on certificate renewal. Reusing private keys can help if you intend to use [HPKP](https://developer.mozilla.org/en-US/docs/Web/HTTP/Public_Key_Pinning), but please note that HPKP has been deprecated by Google's Chrome and that it is therefore strongly discouraged to use it at all.
*`DHPARAM_BITS` - Change the key size of the RFC7919 Diffie-Hellman group used by the container from the default value of 4096 bits. Supported values are `2048`, `3072` and `4096`. The DH group file will be located in the container at `/etc/nginx/certs/dhparam.pem`. Mounting a different `dhparam.pem` file at that location will override the RFC7919 group creation by the acme-companion container. **COMPATIBILITY WARNING**: some older clients (like Java 6 and 7) do not support DH keys with over 1024 bits. In order to support these clients, you must provide your own `dhparam.pem`.
*`DHPARAM_SKIP` - Set it to `true` to disable the Diffie-Hellman group creation by the container entirely.
*`CA_BUNDLE` - This is a test only variable [for use with Pebble](https://github.com/letsencrypt/pebble#avoiding-client-https-errors). It changes the trusted root CA used by `acme.sh`, from the default Alpine trust store to the CA bundle file located at the provided path (inside the container). Do **not** use it in production unless you are running your own ACME CA.
*`CERTS_UPDATE_INTERVAL` - 3600 seconds by default, this defines how often the container will check if the certificates require update.
*`ACME_PRE_HOOK` - The provided command will be run before every certificate issuance. The action is limited to the commands available inside the **acme-companion** container. For example `--env "ACME_PRE_HOOK=echo 'start'"`. For more information see [Pre- and Post-Hook](./Hooks.md)
*`ACME_POST_HOOK` - The provided command will be run after every certificate issuance. The action is limited to the commands available inside the **acme-companion** container. For example `--env "ACME_POST_HOOK=echo 'end'"`. For more information see [Pre- and Post-Hook](./Hooks.md)
*`ACME_HTTP_CHALLENGE_LOCATION` - Previously **acme-companion** automatically added the ACME HTTP challenge location to the nginx configuration through files generated in `/etc/nginx/vhost.d`. Recent versions of **nginx-proxy** (>= `1.6`) already include the required location configuration, which remove the need for **acme-companion** to attempt to dynamically add them. If you're running and older version of **nginx-proxy** (or **docker-gen** with an older version of the `nginx.tmpl` file), you can re-enable this behaviour by setting `ACME_HTTP_CHALLENGE_LOCATION` to `true`.
