# DNS Domains You can point **multiple** DNS Records and thus domains to your fylr. But keep in mind: * fylr always has only *one* **main** DNS domain, configured in fylr.yml's `externalURL`, and fylr will redirect to this URL and use it for its image URLs. * The domain in `externalURL` has to be part of your fylr license. Except when testing as the fylr root user or on localhost. * If fylr shall react to additional domains besides the one main domain, make sure that these are also present in the certificate that fylr uses. * If you let fylr retrieve the certificate automatically, you need to configure them as `additionalDomains` in fylr.yml. See [HTTPS](/for-system-administrators/configuration/http-and-https.md) for examples and details about using certificates. ### **Changes** to the main domain * Licenses are bound to domains so make sure you have a license for the new main domain configured as `externalURL`. * Make sure that you either have a certificate for the new domain or to let fylr automatically retrieve a certificate for the new domain. And optionally, `additionalDomains`, as mentioned above. * When you change fylr's main domain: * configured it as `externalURL` in `fylr.yml` and restart fylr * you need to do a re-index: Surf to **https\://**fylr.example.com**/inspect/system/** (login as root) A re-index likely takes only minutes, but also might take hours, if you have a lot of objects. * During that re-index, even if it is running in the background, preview images **will not be visible**. Only after the re-index the images are prepared and working, with the new domain. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.fylr.io/for-system-administrators/configuration/dns-domains.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.