Ports and Certificates

Ports and Certificates


For HTTP requests, by default the Clace service listens on port 25222, on the localhost( interface. This means the HTTP port can be accessed from the same machine, it cannot be accessed remotely. To configure this, update the config file

host = "" # bind to localhost by default for HTTP
port = 25222 # default port for HTTP

to desired values. Port 0 means bind to any available port. Port -1 means disable HTTP access. Use host as to bind to all available interfaces.


For HTTPS requests, the Clace service listens on port 25223 by default, on the any( interface. This means the HTTPS port can be accessed from the same machine and also remotely. The various HTTPS config settings are:

# HTTPS port binding related Config
host = "" # bind to all interfaces (if port is >= 0)
port = 25223 # port for HTTPS
enable_cert_lookup = true # enable looking for domain specific certificate files on disk
service_email = "" # email address for registering with Let's Encrypt. Set a value to enable automatic certs
use_staging = true # use Let's Encrypt staging server
cert_location = "$CL_HOME/config/certificates" # where to look for existing certificate files
storage_location = "$CL_HOME/run/certmagic" # where to cache dynamically created certificates

Port 0 means bind to any available port. Port -1 means disable HTTPS access.

Using the HTTPS port is recommended even for the local environment. HTTP/2 works with HTTPS only. Server Sent Events (SSE) are used by Clace for live reload of dev apps, SSE works best with HTTP/2. Without HTTP/2, there can be connection limit issues with HTTP causing connections from browser to Clace server to hang.

TLS Certificates

In the default configuration, where service_email is empty, certmagic integration is disabled. The certificate handling behavior is:

  • $CL_HOME/config/certificates is looked up for a crt and key file in the PEM format matching the domain name as passed to the server. If a matching certificate is found, that is used.
  • If no domain specific certificate is found, then the default certificate default.crt and default.key are looked up. If found, that is used.
  • If default certificate is not found, then a self-signed default certificate is auto created in the certificates folder.

The intent is to allow custom certificates to be placed in the certificate folder, which will be used. If not found, a self-signed certificate is created and used. For example, if files example.com.crt and example.com.key are found in the certificates folder, those are used for example.com domain.

Dev Env Certificates

For local dev environment, using the auto generated certs will result in browser warnings when connecting to the HTTPS port. To avoid this, use a tool like mkcert to generate root CA for local env. Install mkcert and then run

mkcert -install
mkcert example.com "*.example.com" example.test localhost ::1

cp ./example.com+5.pem $CL_HOME/config/certificates/default.crt
cp ./example.com+5-key.pem $CL_HOME/config/certificates/default.key

The mkcert generated certificates signed with the local CA will be used after the next Clace server restart.

For local env, wildcard DNS will not work without tools like dnsmasq. An easier alternative is to add /etc/hosts entries as required mapping to Using url path routing instead of domain based routing for local env is a convenient option.

Enable Automatic Signed Certificate

Clace uses the certmagic library for fully-managed TLS certificate issuance and renewal for production deployment. Certmagic is disabled by default. To enable, the pre-requisites are:

  • The https config is using 443 as the port number. Running on privileged ports requires additional setup
  • There is an DNS entry created pointing your host name or domain wildcard to the IP address of the host running the Clace server. This has to be done in your DNS provider config.
  • Port 443 is reachable from the public internet. This has to be done in your infrastructure provider network settings.

Once the pre-requisites are met, set the service_email config parameter to your email address. This enables certmagic based certificate creation. The config will look like:

# HTTPS port binding related Config
host = ""
port = 443
enable_cert_lookup = true # enable looking for domain specific certificate files on disk
service_email = "MY_EMAIL@example.com" # CHANGE to your email address
use_staging = true # CHANGE to false for production
cert_location = "$CL_HOME/config/certificates"
storage_location = "$CL_HOME/run/certmagic"

Test out the certificate creation by sending HTTPS requests to port 443. If the certificate is getting created, change use_staging to false. Let’s Encrypt has strict rate limits, use the staging config to ensure that the pre-requisites are met before using the production config.

With this config, certmagic is used to create certificates for all HTTPS requests. Self signed certificates and enable_cert_lookup property are not used when certmagic is enabled.

Privileged Ports

On Linux, binding to low ports is disabled for non-root users. To enable binding to port 80 for HTTP and 443 for HTTPS, run the command

sudo setcap cap_net_bind_service=+ep /path/to/clace_binary

This would be required after any new build or update of the Clace binary.


  • Please provide a valid email address in service_email. This allows you to receive expiration emails and also allows the CA to contact you if required.
  • Start the configuration with staging use_staging = true, change to production config use_staging = false after ensuring that DNS and networking is working fine.
  • If port 0 is used, the service will bind to any available port. Look at the stdout or logs to find the port used. Clients would have to be updated after every server restarted to point to the new port.
  • Only the TLS-ALPN challenge is enabled in Clace. The HTTP and DNS based challenges are not supported currently.
  • If Clace is running behind a load balancer, ensure that the load balancer is doing TLS pass-through. If TLS termination is done in the load balancer, then the automatic certificate management done by Clace through certmagic will not work.