Last updated 11th May 2021

Let's Encrypt

All environments on Web PaaS support both HTTP and HTTPS automatically. Production TLS certificates are provided by Let's Encrypt. You may alternatively provide your own TLS certificate from a 3rd party issuer of your choice at no charge from us.

Let’s Encrypt TLS Certificates are valid for 90 days and Web PaaS will automatically renew them 28 days before expiration to avoid HTTPS interruptions. If a renewal is available and needed, the environment will automatically redeploy to renew the certificate. As no new build is required the process should take at most a few seconds. The deploy and post-deploy hook will be run during this process.

Web PaaS provides managed service and runtime containers for your projects - security and system upgrades to those containers are applied automatically by us in the background. Whether or not an upgrade needs to be applied is judged during redeploys, but also during this renewal process. That means that most of the time renewals take a few seconds unless upgrades are available for your containers. In those cases, containers will be rebooted and the process will take a little longer.

If you are using a custom TLS certificate, seven days before it expires Web PaaS will issue a Let's Encrypt certificate and replace the custom certificate with it in order to avoid interruption in service. If you wish to continue using the custom certificate, replace it with an updated certificate more than seven days before it expires.

TLS certificates are often still called SSL certificates. TLS is a newer encryption system that has replaced SSL, but the name SSL is still widely recognized. In practice, they mean the same thing today, but TLS is the more correct term.


Web PaaS recommends using HTTPS requests for all sites exclusively. Doing so provides better security, access to certain features that web browsers only permit over HTTPS, and access to HTTP/2 connections on all sites which can greatly improve performance.

How HTTPS redirection is handled depends on the routes you have defined. Web PaaS recommends specifying all HTTPS routes in your routes.yaml file. That will result in all pages being served over TLS, and any requests for an HTTP URL will automatically be redirected to HTTPS.

    type: upstream
    upstream: "app:http"

    type: redirect
    to: "https://{default}/"

Specifying only HTTP routes will result in duplicate HTTPS routes being created automatically, allowing the site to be served from both HTTP and HTTPS without redirects.

Although Web PaaS does not recommend it, you can also redirect HTTPS requests to HTTP explicitly to serve the site over HTTP only. The use cases for this configuration are few.

    type: upstream
    upstream: "app:http"

    type: redirect
    to: "http://{default}/"

    type: redirect
    to: "http://{default}/"

    type: redirect
    to: "http://{default}/"

More complex routing logic is also possible if the situation calls for it.

Let's Encrypt has a limit of 100 TLS certificates per environment. If you define both a {default} and www.{default} route for each domain you use, that will give you a limit of 50 domains. Adding more than that will result in a warning on deploy and some domains will not be issued a TLS certificate. If you need more than that, we recommend obtaining additional certificates or a wildcard certificate from another TLS provider. Alternatively, consider splitting your project up into multiple discrete Web PaaS projects.

TLS configuration

Optionally, it's possible to further refine how secure TLS connections are handled on your cluster via the tls route property.

    type: upstream
    upstream: app:http
        # ...


Setting a minimum version of TLS will cause the server to automatically reject any connections using an older version of TLS. Rejecting older versions with known security vulnerabilities is necessary for some security compliance processes.

    min_version: TLSv1.3

The above configuration will result in requests using older TLS versions to be rejected. Legal values are TLSv1.2 and TLSv1.3. TLS versions older than 1.2 are not supported by Web PaaS and will be rejected regardless of the setting here.

Note that if multiple routes for the same domain have different min_versions specified, the highest specified will be used for the whole domain.


HTTP Strict Transport Security (HSTS) is a mechanism for telling browsers to use HTTPS exclusively with a particular website. You can toggle it on for your site at the router level without having to touch your application, and configure it's behavior from routes.yaml.

        enabled: true
        include_subdomains: true
        preload: true

There are three sub-properties for the strict_transport_security property:

  • enabled: Can be true, false, or null. Defaults to null. If false, the other properties wil be ignored.
  • include_subdomains: Can be true or false. Defaults to false. If true, browsers will be instructed to apply HSTS restrictions to all subdomains as well.
  • preload: Can be true or false. Defaults to false. If true, Google and others may add your site to a lookup reference of sites that should only ever be connected to over HTTPS. Many although not all browsers will consult this list before connecting to a site over HTTP and switch to HTTPS if instructed. Although not part of the HSTS specification it is supported by most browsers.

If enabled, the Strict-Transport-Security header will always be sent with a lifetime of 1 year. The Mozilla Developer Network has more detailed information on HSTS.

Note: If multiple routes for the same domain specify different HSTS settings, the entire domain will still use a shared configuration. Specifically, if any route on the domain has strict_transport_security.enabled set to false, HSTS will be disabled for the whole domain. Otherwise, it will be enabled for the whole domain if at least one such route has enabled set to true. As this logic may be tricky to configure correctly we strongly recommend picking a single configuration for the whole domain and adding it on only a single route.

Client authenticated TLS

In some non-browser applications (such as mobile applications, IoT devices, or other restricted-client-list use cases), it is beneficial to restrict access to selected devices using TLS. This process is known as client-authenticated TLS, and functions effectively as a more secure alternative to HTTP Basic Auth.

By default, any valid TLS cert issued by one of the common certificate issuing authorities will be accepted. Alternatively, you can restrict access to TLS certs issued by just those certificate authorities you specify, including a custom authority. (The latter is generally only applicable if you are building a mass-market IoT device or similar.) To do so, set client_authentication required and then provide a list of the certificates of the certificate authorities you wish to allow.

    client_authentication: "require"
        - !include
            type: string
            path: root-ca1.crt
        - !include
            type: string
            path: root-ca2.crt

In this case, the certificate files are resolved relative to the .platform directory. Alternatively, the certificates can be specified inline in the file:

    client_authentication: "require"
        - |
            -----BEGIN CERTIFICATE-----
            ### Several lines of random characters here ###
            -----END CERTIFICATE-----
        - |
            -----BEGIN CERTIFICATE-----
            ### Several lines of different random characters here ###
            -----END CERTIFICATE-----

Let's Encrypt limits, errors, and branch names

You may encounter Let's Encrypt certificates failing to provision after the build hook has completed:

Provisioning certificates
  Validating 2 new domains
  E: Error provisioning the new certificate, will retry in the background.
  (Next refresh will be at 2020-02-13 14:29:22.860563+00:00.)
  Environment certificates
W: Missing certificate for domain www.<PLATFORM_ENVIRONMENT>-<PLATFORM_PROJECT>.<REGION>
W: Missing certificate for domain <PLATFORM_ENVIRONMENT>-<PLATFORM_PROJECT>.<REGION>

One reason that this can happen has to do with the limits of Let's Encrypt itself, which caps off at 64 characters for URLs. If your TLS certificates are not being provisioned, it's possible that the names of your branches are too long, and the environment's generated URL goes over that limit.

At this time, generated URLs have the following pattern:

  • PLATFORM_PROJECT = 13 characters
  • REGION = 13 characters
  • = 15 characters
  • extra characters (. & -) = 4 characters

This breakdown leaves you with 12-15 characters to work with naming your branches (PLATFORM_BRANCH) without going over the 64 character limit, dependent on the region. Since this pattern for generated URLs will remain similar, but could change slightly over time, it's our recommendation to use branch names with a maximum length between 6 and 11 characters.

DNS Challenge

To be able to provide a valid SSL-certificate, Let's Encrypt needs to make sure that the requester is entitled to receive the SSL-certificate it asked for (usually through the presence of a specific token on the DNS zone of that domain).

This ownership verification is achieved through the so called Challenge step, more background information can be found in the Let's Encrypt Documentation.

Sometimes, that verification fails which will result in the following error-message: Couldn't complete challenge [HTTP01: pending | DNS01: pending | TLSALPN01: pending]

For the DNS challenge to work, domains and subdomains should point directly to your Web PaaS cluster (unless using a CDN). Otherwise, you will see the following error:

  E: Error validating domain Couldn't complete challenge [HTTP01: pending | DNS01: pending | TLSALPN01: pending]
  Unable to validate domains, will retry in the background.

Note that DNS changes can take up to 24-48 hours to propagate. If you have waited the 24-48 hours, properly configured the subdomain, and are still seeing an error of this type, redeploying the impacted environment will usually solve the issue.

If the issue persists, you could also verify if an outage is currently ongoing on let's encrypt's side. If that is not the case, please open a support ticket.

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