Possible to perform scheduled cron jobs in a deployed node REST API server?

Questions / Help
1

Hello, I have a REST API server deployed with fly. I want to create a new record in my Mongo database at a specific time every day, which I assume isn’t possible with something like node-cron since the api server wouldn’t be running 24/7. So I followed the steps in this guide Crontab with Supercronic · Fly Docs.

Unfortunately I’m not very familiar with Docker files or what Fly does under the hood, so I’ve tried to modify the files so that in theory I could run a specific javascript file everyday:

Dockerfile:

# Latest releases available at https://github.com/aptible/supercronic/releases
ENV SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.2.1/supercronic-linux-amd64 \
    SUPERCRONIC=supercronic-linux-amd64 \
    SUPERCRONIC_SHA1SUM=d7f4c0886eb85249ad05ed592902fa6865bb9d70

RUN curl -fsSLO "$SUPERCRONIC_URL" \
 && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
 && chmod +x "$SUPERCRONIC" \
 && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
 && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic

# You might need to change this depending on where your crontab is located
COPY crontab crontab

FROM node:17-alpine as build-image
WORKDIR /usr/src/app
COPY package*.json ./
COPY tsconfig.json ./
COPY ./src ./src
RUN npm ci
RUN npx tsc

FROM node:17-alpine
WORKDIR /usr/src/app
COPY package*.json ./
COPY --from=build-image ./usr/src/app/dist ./dist
RUN npm ci --production
COPY . .
EXPOSE 8080
CMD [ "node", "dist/app.js" ]

fly.toml:

app = ""
kill_signal = "SIGINT"
kill_timeout = 5
primary_region = "mia"
processes = []

[build]

[env]
  PORT = "8080"

[experimental]
  auto_rollback = true

[[services]]
  processes = ["app", "web"]
  http_checks = []
  internal_port = 8080
    processes = ["app", "web"]
  protocol = "tcp"
  script_checks = []
  [services.concurrency]
    hard_limit = 25
    soft_limit = 20
    type = "connections"

  [[services.ports]]
    force_https = true
    handlers = ["http"]
    port = 80

  [[services.ports]]
    handlers = ["tls", "http"]
    port = 443

  [[services.tcp_checks]]
    grace_period = "1s"
    interval = "15s"
    restart_limit = 0
    timeout = "2s"

[processes]
  # The command below is used to launch a Rails server; be sure to
  # replace with the command you're using to launch your server.
  web = "node dist/src/scripts/dailyReset.js"
  cron = "supercronic /app/crontab"

This causes the deployment to fail at this stage:
Error: failed to fetch an image or build from source: error building: failed to solve with frontend dockerfile.v0: failed to create LLB definition: no build stage in current context

And I first wanted to confirm whether what I’m trying to do was even possible, or if I’d have to create a different app specifically to perform this one scheduled job. Thank you.

2

Your Dockerfile needs to start with a FROM statement, but even if you got it working you would need the machine to be running for the cron job tasks to fire.

scheduled machines may be of interest.

3

Thank you for the reply. I would love to use scheduled machines but unfortunately I need the task to execute at a specific time everyday which seems difficult to do with how scheduled machines is set up. I’ll have to look into deploying the scheduler separately.

4

As a follow-up question, if I were to look into using scheduled machines, would there be a way for me to get the precise date/time when it runs? Or would I have to just grab the time when the machine starts and calculate from there?

5

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