Dokku can host several independent applications on one server while all of them use the public HTTP and HTTPS ports. The reliable pattern is to give every app a unique hostname, point each DNS record to the server, deploy each app under its own Dokku app name, and assign its domain with the domains plugin. Dokku’s nginx virtual hosts then route app1.example.com and app2.example.net to different containers, even when those containers listen on different internal ports.
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How Dokku routes several apps through ports 80 and 443
A Dokku host has one public network interface, but it does not need one public port per application. Incoming requests arrive at nginx on ports 80 (HTTP) or 443 (HTTPS). nginx examines the request hostname and forwards it to the Dokku app whose domain list contains that hostname. Each app keeps its own container, process configuration, environment, deployment history and proxy mapping.
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For example, these requests can share one server:
https://app1.example.comroutes to the container runningapp1.https://app2.example.netroutes to the container runningapp2.https://api.example.comcan route to a third app, provided that hostname is assigned to it.
The public ports remain 80 and 443. The container ports can differ, such as app1 listening on 3000 and app2 on 8080. Dokku’s proxy layer maintains the per-app mapping. There is no published Dokku statistic that defines a maximum number of applications per host; the practical limit depends on the server’s CPU, memory, storage, network capacity and the workloads you deploy.
Choose the hostname arrangement before deploying
Decide whether each application will use a separate registered domain, a subdomain under one domain, or several hostnames for one application. The choice affects DNS administration, certificates and how independently you can operate each app.
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| Arrangement | Example | DNS responsibility | Certificate implication | Operational fit |
|---|---|---|---|---|
| Separate domains | app1.example.com and app2.example.net |
You control DNS for each domain and point every name to the Dokku server | Each app’s certificate covers the names in that app’s domain list | Strong separation for unrelated products, teams or customers |
| Subdomains of one domain | app1.example.com and app2.example.com |
One DNS zone contains records for all apps | Each app can still have its own certificate for its assigned hostname | Convenient when one organization owns the whole namespace |
| Multiple names on one app | www.example.com and example.com |
Both names must resolve to the server and be assigned to the same app | The certificate must include every assigned name; re-enable certificate provisioning after changes | Useful for aliases, canonical redirects or an additional customer domain |
Dokku’s global domain supplies defaults for newly configured apps. The subdomain is inferred from the pushed application name, while the domain suffix is set during initial Dokku configuration. Explicit per-app domains override those defaults, so use domains:set when the hostname must be precise or when apps use different parent domains.
Prerequisites and a safe deployment plan
- A Dokku server with a public IPv4 address and, if used, a public IPv6 address.
- Administrative access to create DNS records and run Dokku commands on the host.
- A unique Dokku app name for every application.
- A deployable source repository, Dockerfile or Docker image. Dokku supports Heroku buildpacks, Dockerfiles and Docker images.
- DNS A records, and AAAA records when IPv6 is enabled, for every hostname.
- An application that listens on the port Dokku maps for it. If it uses a non-standard container port, plan to verify the proxy mapping after deployment.
Use a written inventory before you start. Record the Dokku app name, every hostname, the DNS record type and target, the expected container port, and whether the app needs HTTP only or HTTPS. This prevents a common mistake: configuring a certificate or domain for a name that still points somewhere else.
Step 1: Point every domain or subdomain at Dokku
Create an A record for each hostname that targets the Dokku server’s public IPv4 address. Add an AAAA record only when the server is reachable over IPv6 and your firewall and application path support it. For separate domains, repeat this in each domain’s DNS zone. For subdomains, add records such as app1 and app2 to the parent zone.
Wait until public DNS resolves each name to the Dokku host before attempting normal HTTP routing or automated certificate issuance. Dokku’s deployment documentation specifically requires all app domains to point to the server’s public IP for automated Let’s Encrypt validation. A stale record, an old hosting provider’s address or a conflicting AAAA record can cause validation to reach the wrong machine.
- Check the A record from more than one network if possible.
- Check the AAAA record separately; an incorrect IPv6 target can make some clients fail even when IPv4 works.
- Do not assume that a DNS change is visible everywhere immediately; verify the authoritative zone and allow normal DNS caching to expire.
Step 2: Create and deploy each Dokku app
Use a different Dokku app name for each application. The app name is part of the Git remote and is also used by Dokku when it creates the application’s resources.
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Deploy the first repository
- From the local repository for the first application, add a Dokku remote:
git remote add dokku dokku@SERVER:app1. - Push the branch you deploy:
git push dokku main. - Let Dokku build and release the application using its buildpack, Dockerfile or image workflow.
Deploy the second repository
- From the second application’s repository, add a separate remote:
git remote add dokku dokku@SERVER:app2. - Push its branch:
git push dokku main. - Confirm that the second build completes independently of the first app.
If both repositories are on the same workstation, keep the remotes in the correct repository. Accidentally pushing the second codebase to app1 updates app1 rather than creating a new application.
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Set the primary hostname for each app on the Dokku host:
dokku domains:set app1 app1.example.com
dokku domains:set app2 app2.example.netWhen an app needs an additional hostname, add it without replacing the existing list:
dokku domains:add APP extra.exampleUse domains:set when you want to replace the app’s domain list with a deliberate set of names. Use domains:add for an alias such as a www hostname, a legacy name or a second customer-controlled domain. Every name in the list must have DNS pointing to this Dokku server before it can be reached correctly.
Verify the domain list
dokku domains:report app1
dokku domains:report app2The report is the authoritative check that Dokku has stored the names you intended. If a hostname is missing, correct the domain list before troubleshooting browsers or certificates. If the report contains an unwanted default domain, replace the list explicitly with domains:set.
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Step 4: Verify proxy and container-port mappings
Most web applications expose the port expected by Dokku’s normal proxy configuration. Problems appear when an application listens on a non-standard container port or when a domain was added before the application was deployed. Dokku warns that a domain configured before deployment may create a mapping that does not automatically match a later non-standard port.
Inspect each app’s mapping:
dokku ports:report app1
dokku ports:report app2Compare the reported mapping with the port on which the application actually listens inside its container. A mapping such as http:80:3000 means public HTTP traffic is accepted on port 80 and forwarded to container port 3000. For HTTPS, the equivalent pattern is https:443:3000. The exact internal port must match the application process; changing only the external URL does not make a process listening on 8080 respond on 3000.
When the mapping is wrong
- Confirm the application’s listen port in its runtime or start command.
- Inspect the output of
dokku ports:report APPand identify the target container port. - Correct the Dokku port configuration using the port-management commands appropriate to your installed Dokku version, then redeploy or restart the app as required.
- Recheck the report and test the hostname again after nginx reloads.
Do not solve a hostname collision by assigning another public port when the goal is ordinary domain-based hosting. Multiple apps can share 80 and 443; they need distinct hostnames and correct internal mappings, not separate public HTTP ports.
Step 5: Enable HTTPS for each app
Automated HTTPS is optional. Dokku can also use imported certificates, but automated Let’s Encrypt issuance requires every domain on the app to resolve to the server’s public IP. Install the optional Let’s Encrypt plugin, configure its global email address, and then enable it separately for each app.
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dokku letsencrypt:enable app2The plugin requests certificates for the names in each app’s domain list and reloads nginx after successful issuance. Enable certificates only after DNS is live and the app’s HTTP route works; otherwise validation can fail because the challenge reaches the wrong server or an incorrect port mapping.
Adding a hostname after HTTPS is enabled
A certificate’s subject-alternative-name list must contain every hostname you expect clients to use. When you add or change domains, run dokku letsencrypt:enable APP again so the certificate is reissued with the updated names. Merely adding a name with domains:add does not retroactively expand an already issued certificate.
Apply this sequence whenever an app gains an alias:
- Add the DNS record and wait for it to resolve to the Dokku server.
- Add the hostname with
dokku domains:add APP new.example. - Verify the complete list with
dokku domains:report APP. - Run
dokku letsencrypt:enable APPagain. - Test both the original and new HTTPS names.
Complete two-app command pattern
The following is a compact sequence for two repositories. Replace the placeholders with your server, app names, domains and actual branch.
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git remote add dokku dokku@SERVER:app1
git push dokku main
# Deploy app2
git remote add dokku dokku@SERVER:app2
git push dokku main
# Assign separate hostnames
dokku domains:set app1 app1.example.com
dokku domains:set app2 app2.example.net
# Inspect domains and proxy mappings
dokku domains:report app1
dokku domains:report app2
dokku ports:report app1
dokku ports:report app2
# Enable certificates after DNS is live
dokku letsencrypt:enable app1
dokku letsencrypt:enable app2The commands do not infer your DNS records, application listen ports or certificate requirements. Those values must match the deployment you actually made.
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The hostname shows another site or a default response
- Check the hostname’s A and AAAA records; one may still point to an old server.
- Run
dokku domains:report APPand confirm the exact spelling of the hostname. - Check that no other Dokku app owns the same domain.
- Allow DNS caches to expire, then test again.
HTTP reaches the app but HTTPS fails
- Confirm the Let’s Encrypt plugin completed successfully for that app.
- Check that every assigned name resolves to this server; certificate validation covers the whole domain list.
- If the domain list changed, run
dokku letsencrypt:enable APPagain. - Inspect the app’s port report for an incorrect HTTPS target.
The app returns a proxy error or connection refusal
- Verify that the process is listening on the container port Dokku reports.
- Check whether the app binds to the container interface rather than only to localhost.
- Correct the non-standard mapping and redeploy or restart as appropriate.
Only some users can reach the site
- Compare IPv4 and IPv6 DNS results. An incorrect AAAA record can affect IPv6-capable clients while IPv4 tests pass.
- Check firewall rules for both public ports 80 and 443.
- Retest after DNS propagation and certificate issuance have completed.
Operational decisions that prevent future outages
Keep app names and domains predictable
Use a consistent naming scheme such as customer-portal, api and staging. Map each name to an explicit hostname instead of relying indefinitely on the global domain default. This makes migrations and audits easier.
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Separate production and non-production hostnames
Give staging and production different domains or subdomains and separate Dokku app names. A deployment to staging then cannot accidentally replace the production app’s code or domain mapping.
Track every alias
Keep a list of all names assigned with domains:add. Removing a DNS record without removing the Dokku domain can leave a stale certificate name or an unexpected routing rule. When an alias is retired, update DNS, the Dokku domain list and the certificate configuration together.
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Separate Dokku apps receive separate routing and deployment configuration, but they still share the host’s physical resources. CPU, memory, disk and network contention can affect every app. Dokku’s official documentation does not publish a universal app-per-server limit or performance benchmark, so size the server for your actual workload and monitor it in operation.
Checklist before declaring the deployment complete
- Every app has a unique Dokku app name.
- Every hostname has the correct A record, and an AAAA record only when IPv6 is intentionally supported.
- DNS resolves each hostname to the Dokku server’s public address.
- Each repository was pushed to the intended Dokku Git remote.
dokku domains:report APPshows the complete, correct domain list.dokku ports:report APPmatches the application’s actual container listen port.- HTTP requests route to the intended app on port 80.
- Let’s Encrypt is enabled for every app that needs HTTPS.
- After any domain change, certificate enablement was run again.
- Both IPv4 and IPv6 paths, if enabled, have been tested.
What to remember
Deploying multiple domains on one Dokku server is a hostname-routing problem, not a public-port allocation problem. Deploy each application under a unique app name, point every DNS name to the server, assign explicit per-app domains, verify internal port mappings, and issue certificates only after DNS is correct. nginx can then serve many independent apps through ports 80 and 443 while Dokku forwards each request to the correct container.
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