Failed due to unhealthy allocations - HTTP Error 502 after trying to deploy Express application

Hey team, been playing around a bit with Fly recently and writing a blog post to explain how to get an Express app spun up.

I’m a big container noob so mostly just following along with docs, running commands and seeing what happens. I know there’s a troubleshooting guide but a lot of it’s over my head, so my apologies for not RTFM and I’m sure I’m making a silly mistake somewhere along the way.

I’ve got this current project that’s erroring out:


const express = require("express")
const app = express()

const port = process.env.PORT || 3000

  "/", (req, res) => {
    greeting = "<h1>ajcwebdev-fly</h1>"

  () => console.log(`Hello from port ${port}!`)

Run server

node index.js
Hello from port 3000!


FROM node:14-alpine
WORKDIR /usr/src/app
COPY package*.json ./
RUN npm i
COPY . ./
CMD [ "node", "index.js" ]



Launch app on Fly

flyctl launch --name ajcwebdev-fly --region sjc
Creating app in /Users/ajcwebdev/ajcwebdev-fly
Scanning source code
Detected NodeJS app
Using the following build configuration:
	Builder: heroku/buildpacks:20
Automatically selected personal organization: Anthony Campolo
Created app ajcwebdev-fly in organization personal
Wrote config file fly.toml
Your app is ready. Deploy with `flyctl deploy`


app = "ajcwebdev-fly"

kill_signal = "SIGINT"
kill_timeout = 5


  allowed_public_ports = []
  auto_rollback = true

  http_checks = []
  internal_port = 8080
  protocol = "tcp"
  script_checks = []

  hard_limit = 25
  soft_limit = 20
  type = "connections"

  handlers = ["http"]
  port = 80

  handlers = ["tls", "http"]
  port = 443

  grace_period = "1s"
  interval = "15s"
  restart_limit = 6
  timeout = "2s"

Deploy application with flyctl deploy

flyctl deploy
Deploying ajcwebdev-fly
==> Validating app configuration
--> Validating app configuration done
TCP 80/443 ⇢ 8080
==> Creating build context
--> Creating build context done
==> Building image with Docker
Sending build context to Docker daemon  37.38kB
[+] Building 14.3s (10/10) FINISHED                                                                                    
 => [internal] load remote build context                                                                          0.0s
 => copy /context /                                                                                               0.1s
 => [internal] load metadata for                                                 1.8s
 => [1/5] FROM  6.3s
 => => resolve  0.0s
 => => sha256:59857143b3784bf4afb6f93a8082180e88faa75a8efee07147589552843e5433 36.21MB / 36.21MB                  5.0s
 => => sha256:9f27d30bcf3a07255d5080e92a199cd8cf154bb91526f9519b2355687cd15eab 2.24MB / 2.24MB                    1.6s
 => => sha256:fb6cb918cc72869bd625940f42a7d8ae035c4e786d08187b94e8b91c6a534dfd 1.43kB / 1.43kB                    0.0s
 => => sha256:5c33bc6f021453ae2e393e6e20650a4df0a4737b1882d389f17069dc1933fdc5 1.16kB / 1.16kB                    0.0s
 => => sha256:f5f48375fc5d0df18a96d337019e7dc4e99efd4d98f9e8ab53af74c56de91de3 6.53kB / 6.53kB                    0.0s
 => => sha256:ddad3d7c1e96adf9153f8921a7c9790f880a390163df453be1566e9ef0d546e0 2.82MB / 2.82MB                    0.6s
 => => extracting sha256:ddad3d7c1e96adf9153f8921a7c9790f880a390163df453be1566e9ef0d546e0                         0.1s
 => => sha256:be8cf85a075db5d053c8652e924886e96d26ed77c1cce39ad75e22ae41de5236 281B / 281B                        0.9s
 => => extracting sha256:59857143b3784bf4afb6f93a8082180e88faa75a8efee07147589552843e5433                         1.0s
 => => extracting sha256:9f27d30bcf3a07255d5080e92a199cd8cf154bb91526f9519b2355687cd15eab                         0.1s
 => => extracting sha256:be8cf85a075db5d053c8652e924886e96d26ed77c1cce39ad75e22ae41de5236                         0.0s
 => [2/5] WORKDIR /usr/src/app                                                                                    0.1s
 => CACHED copy /context /                                                                                        0.0s
 => [3/5] COPY package*.json ./                                                                                   0.0s
 => [4/5] RUN npm i                                                                                               5.9s
 => [5/5] COPY . ./                                                                                               0.0s
 => exporting to image                                                                                            0.1s
 => => exporting layers                                                                                           0.1s
 => => writing image sha256:2e86fa4eedeb4e7b4a5ece2b5167e1c7a6e810bc1c8c0a69463ca57bc8ea2698                      0.0s
 => => naming to                                              0.0s
--> Building image done
==> Pushing image to fly
The push refers to repository []
e503c0f3789e: Pushed 
efbef288213d: Pushed 
dea459947eea: Pushed 
f74349670ae4: Pushed 
87f6a206d8c2: Pushed 
efe9f72a5423: Pushed 
ffa572135c58: Pushed 
9a5d14f9f550: Pushed 
deployment-1627521878: digest: sha256:38dbfc7e0441f180702f1ebc763c621d85c39818c0e487f3ee99d4603ef42d9b size: 1992
--> Pushing image done
Image size: 120 MB
==> Creating release
Release v0 created

You can detach the terminal anytime without stopping the deployment
Monitoring Deployment

1 desired, 1 placed, 0 healthy, 1 unhealthy [restarts: 2] [health checks: 1 total, 1 critical]
v0 failed - Failed due to unhealthy allocations - no stable job version to auto revert to
Failed Instances

==> Failure #1

  ID            = 808d096b             
  Version       = 0                    
  Region        = sjc                  
  Desired       = run                  
  Status        = running              
  Health Checks = 1 total, 1 critical  
  Restarts      = 2                    
  Created       = 4m7s ago             

Recent Events
TIMESTAMP            TYPE             MESSAGE                                                         
2021-07-29T01:26:15Z Received         Task received by client                                         
2021-07-29T01:26:15Z Task Setup       Building Task Directory                                         
2021-07-29T01:26:19Z Started          Task started by client                                          
2021-07-29T01:27:36Z Restart Signaled healthcheck: check "66cf15a97e3a024dadbbfb595963ba3f" unhealthy 
2021-07-29T01:27:39Z Terminated       Exit Code: 130                                                  
2021-07-29T01:27:39Z Restarting       Task restarting in 1.029876556s                                 
2021-07-29T01:27:41Z Started          Task started by client                                          
2021-07-29T01:28:58Z Restart Signaled healthcheck: check "66cf15a97e3a024dadbbfb595963ba3f" unhealthy 
2021-07-29T01:29:01Z Terminated       Exit Code: 130                                                  
2021-07-29T01:29:01Z Restarting       Task restarting in 1.125485629s                                 
2021-07-29T01:29:03Z Started          Task started by client                                          

Recent Logs
2021-07-29T01:27:41Z [info] Configuring firecracker
2021-07-29T01:27:41Z [info] Starting virtual machine
2021-07-29T01:27:41Z [info] Starting init (commit: cc4f071)...
2021-07-29T01:27:41Z [info] Running: ` node index.js` as root
2021-07-29T01:27:41Z [info] 2021/07/29 01:27:41 listening on [fdaa:0:2f5b:a7b:ad1:808d:96b:2]:22 (DNS: [fdaa::3]:53)
2021-07-29T01:27:41Z [info] Hello from port 3000!
2021-07-29T01:27:49Z [warn] Health check status changed 'passing' => 'warning'
2021-07-29T01:27:58Z [error] Health check status changed 'warning' => 'critical'
2021-07-29T01:28:58Z [info] Shutting down virtual machine
2021-07-29T01:28:58Z [info] Sending signal SIGINT to main child process w/ PID 507
2021-07-29T01:28:59Z [info] Main child exited with signal (with signal 'SIGINT', core dumped? false)
2021-07-29T01:28:59Z [info] Starting clean up.
2021-07-29T01:29:02Z [info] Starting instance
2021-07-29T01:29:02Z [info] Configuring virtual machine
2021-07-29T01:29:02Z [info] Pulling container image
2021-07-29T01:29:03Z [info] Unpacking image
2021-07-29T01:29:03Z [info] Preparing kernel init
2021-07-29T01:29:03Z [info] Configuring firecracker
2021-07-29T01:29:03Z [info] Starting virtual machine
2021-07-29T01:29:03Z [info] Starting init (commit: cc4f071)...
2021-07-29T01:29:03Z [info] Running: ` node index.js` as root
2021-07-29T01:29:03Z [info] 2021/07/29 01:29:03 listening on [fdaa:0:2f5b:a7b:ad1:808d:96b:2]:22 (DNS: [fdaa::3]:53)
2021-07-29T01:29:04Z [info] Hello from port 3000!
2021-07-29T01:29:04Z [info] Health check status changed 'critical' => 'passing'
2021-07-29T01:29:08Z [warn] Health check status changed 'passing' => 'warning'
2021-07-29T01:29:17Z [error] Health check status changed 'warning' => 'critical'
2021-07-29T01:30:21Z [info] Shutting down virtual machine
2021-07-29T01:30:21Z [info] Sending signal SIGINT to main child process w/ PID 507
2021-07-29T01:30:22Z [info] Main child exited with signal (with signal 'SIGINT', core dumped? false)
2021-07-29T01:30:22Z [info] Starting clean up.
***v0 failed - Failed due to unhealthy allocations - no stable job version to auto revert to and deploying as v1 

Troubleshooting guide at

flyctl status

flyctl status
  Name     = ajcwebdev-fly          
  Owner    = personal               
  Version  = 0                      
  Status   = dead                   
  Hostname =  

Deployment Status
  ID          = 61205d95-4f62-0abe-5d0c-43680a47eb4f                                           
  Version     = v0                                                                             
  Status      = failed                                                                         
  Description = Failed due to unhealthy allocations - no stable job version to auto revert to  
  Instances   = 1 desired, 1 placed, 0 healthy, 1 unhealthy                                    


flyctl open

flyctl open

1 Like

Do you need to set PORT=8080 in your fly.toml env section?

1 Like

Yep, concur with @pims. It looks like you have to set that port variable under the [env] section.

1 Like

Thanks so much @pims and @rugwirobaker, that did the trick!

  PORT = 8080

1 Like

Here’s the blog post if anyone is interested.

And repo.