Working with Fly Applications

Once you have deployed a Fly application, you can view information about it, give the system secrets to share with it, and associate it with a custom domain.

Viewing Applications

flyctl can reveal useful information about the application:

  • generally about the application configuration
  • specifically about the application deployment
  • and historically with the applications logs

General Information

The info subcommand will reveal the name of the current application, owner, a short status and the application's hostname. There's also details of how the application's ports are mapped under Services.

Finally, it shows the IP Addresses that the application is mapped to. You'll need this information for configuring your custom domains.

flyctl info
  Name     = hellofly
  Owner    = demo
  Version  = 2
  Status   = running
  Hostname =

  app    tcp        80 => 8080 [HTTP]
                    443 => 8080 [TLS, HTTP]

IP Addresses
  TYPE   ADDRESS                                CREATED AT
  v4                          2020-01-17T16:51:23Z
  v6     2a09:8280:1:27a2:d07e:157d:dd9e:87d2   2020-01-17T16:51:24Z

The IP Address information is also available with the flyctl ips list command.

Deployment Status

The status subcommand shows information on when the application was last deployed, what version is deployed and the status of that deployment. If the deployment is currently running, it will also break that down. When the application is deployed, it has what are called allocations in the various global datacenters. The status command will also detail those, including their status, region and when they were created.

flyctl status
  Name     = hellofly
  Owner    = demo
  Version  = 3
  Status   = running
  Hostname =

Deployment Status
  ID          = cf39d39b-9951-0bda-ef3b-795014436095
  Version     = v3
  Status      = successful
  Description = Deployment completed successfully
  Allocations = 1 desired, 1 placed, 1 healthy, 0 unhealthy

  61592bcb   3         ams      run       running   1 passing       39s ago

Viewing Logs

Each Fly application has a log. It includes the console output of all instances of an application. Running fly logs you will display those logs and automatically wait for new log entries. For example, when we run the hellofly sample:

flyctl logs
2020-01-22T14:35:05.933Z 70fda853 ams [info] {"message":"\r","app":3366,"region":"ams","alloc":"70fda853"}
2020-01-22T14:35:05.935Z 70fda853 ams [info] - using env:   export GIN_MODE=release
2020-01-22T14:35:05.935Z 70fda853 ams [info] - using code:  gin.SetMode(gin.ReleaseMode)
2020-01-22T14:35:05.935Z 70fda853 ams [info] {"message":"\r","app":3366,"region":"ams","alloc":"70fda853"}
2020-01-22T14:35:05.936Z 70fda853 ams [info] -
2020-01-22T14:35:05.937Z 70fda853 ams [info] - hellofly.tmpl
2020-01-22T14:35:05.937Z 70fda853 ams [info] {"message":"\r","app":3366,"region":"ams","alloc":"70fda853"}

The log lines consist of an ISO format date and time, the allocation id - the identifier for a particular instance of the app that is running, the region where this instance of the app is running, the level of the attached message and then the actual log line. An entry such as


is recording an unhandled, and in this case incomplete, log line. It is also possible to filter by region or instance id. Consult the flyctl documentation for logs.

Working With Secrets

Passing information, like credentials, to an application is handled through Fly's secrets. Create a secret value with a name and when the application runs, the secret will be available in the applications environment variables. Say we want to pass BANKPASSWORD to our sample application. In our node.js application, we can access that secret by using this code:


All we need to do now is set it, and that's done with flyctl secrets set. It takes a list of names and values as parameters.

flyctl secrets set BANKPASSWORD="M0M0NEY"
VERSION   TYPE      STATUS   DESCRIPTION       USER                 DATE
v1        release            Secrets updated          just now

New instances of the app will now see that value. The secrets set command can also set a number of secrets at the same time and take secrets from STDIN. See the flyctl documentation for secrets set for details.

If you need to know what secrets have been set then flyctl secrets list will show you:

flyctl secrets list
NAME           DIGEST                             DATE
BANKPASSWORD   51e7d4ab982ee30a690d12f15b866370   8m7s ago

It will only show you the name. The value is not shown as it is a secret.

If you need to remove a secret from an app, flyctl secrets unset will remove them by name

flyctl secrets unset BANKPASSWORD
VERSION   TYPE      STATUS   DESCRIPTION       USER                 DATE
v11       release            Secrets updated          just now

Fly and Custom Domains

When you create a Fly app, it is automatically given a sub-domain, based on the app's name. This is great for testing but when you want to go to full production you'll want your application to appear on your own domain and have HTTPS set up for you as it is with your domain. That's where the flyctl certs command comes in. But let's step back before we set up the TLS certificate, to the first step: Directing Traffic To Your Site.

Setting a CNAME Record

The simplest option for directing traffic to your site is to create a CNAME record for your custom domain that points at your host. So if you have a custom domain called and an app called, you can create a CNAME record for's DNS that would look like:


You'll need to configure this with your DNS provider.

Now, accessing will tell the DNS system to look up and return its results for you.

Setting the a Record

The other option is slightly more complicated in that it uses the IP address of the app, rather than its DNS name. The upside is that it is slightly faster.

To start, we need the Fly IP address of our deployed application. To get that, use the flyctl ips list command we covered earlier on.

You'll need to configure this with your DNS provider.

but simply add in an "A Record" for your domain that points to the IP address. Once this is done and propagated through the DNS system, you should be able to connect over unencrypted HTTP to using the domain name:

If we have our domain,

Getting Certified

To enable HTTPS on the domain, you need to get a certificate. Fly does that for you automatically! It starts with creating a certificate for your custom domain with flyctl certs create

flyctl certs add
  Hostname                    =
  Configured                  = true
  Issued                      =
  Certificate Authority       = lets_encrypt
  DNS Provider                = enom
  DNS Validation Instructions =
  DNS Validation Hostname     =
  DNS Validation Target       =
  Source                      = fly
  Created At                  = 0001-01-01T00:00:00Z
  Status                      =

This will start the process of getting a certificate. Run flyctl certs show to get the details needed for your next step:

flyctl certs show
  Hostname                    =
  Configured                  = true
  Issued                      = ecdsa, rsa
  Certificate Authority       = lets_encrypt
  DNS Provider                = enom
  DNS Validation Instructions = CNAME =>
  DNS Validation Hostname     =
  DNS Validation Target       =
  Source                      = fly
  Created At                  = 1m24s ago
  Status                      = Ready

The DNS Validation Instructions are an optional next step. For a short time (minutes) after we start the process of generating the first-ever certificate for your site, trying to load that site with an HTTPS URL will generate errors. If you'd like to make sure those errors aren't ever visible, you can use a DNS challenge to pre-generate the certificate.

To do that, you need to create a CNAME DNS record which for a subdomain _acme-challenge of your domain (the DNS Validation host name) and point it at the DNS Validation Target. The process will depend on your DNS provider. Once complete, and the updated DNS data has propagated, that domain will be queried and confirm you have control of it. Certificates will be generated and installed and you will then be able to access (or whatever your custom domain is called).