Cron Job Fails to Execute cargo run in Docker Container Due to Rustup Configuration

help
1

Hello everyone,

I'm encountering an issue with running a cron job inside a Docker container that uses Rust. The cron job is supposed to execute cargo run every hour, but it fails with the following error:

error: rustup could not choose a version of cargo to run, because one wasn't specified explicitly, and no default is configured.
help: run 'rustup default stable' to download the latest stable release of Rust and set it as your default toolchain.

Here's a brief overview of my setup:

  • Dockerfile: I'm using the rust:1.81.0-slim image and installing necessary packages, including cron.
  • Cron Job: The cron job is set up to run cargo run and log the output to /var/log/cron.log.
  • Manual Execution: When I manually execute the command inside the container, it works perfectly. However, it fails when triggered by cron.

Dockerfile

FROM rust:1.81.0-slim

WORKDIR /usr/src/app

RUN apt-get update && apt-get install -y \
    pkg-config \
    libssl-dev \
    cron \
    iputils-ping \
    ca-certificates \
    curl \
    libcurl4-openssl-dev

COPY . /usr/src/app/

RUN rustup default stable
RUN echo "0 * * * * . $HOME/.cargo/env && cd /usr/src/app && /usr/local/cargo/bin/cargo run >> /var/log/cron.log 2>&1" > /etc/cron.d/rust-cron
RUN chmod 0644 /etc/cron.d/rust-cron
RUN crontab /etc/cron.d/rust-cron

RUN touch /var/log/cron.log

COPY entrypoint.sh /usr/local/bin/entrypoint.sh
RUN chmod +x /usr/local/bin/entrypoint.sh

ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]

I've tried setting the Rust default toolchain using rustup default stable in the Dockerfile, but the issue persists.

Has anyone faced a similar issue or have any suggestions on how to ensure the cron job runs successfully with the correct Rust environment?

Thanks in advance for your help!

2

I don't know if this is your issue, but I've noticed problems in my rust-toolchain.toml when I'm not specific enough about the toolchain. Even a difference such as 1.81 vs 1.81.0 can result in it redownloading the toolchain.

Maybe instead you should be doing rustup default 1.81.0 current stable is 1.82.0 so your image likely already has 1.81 built in and it's going to download the 1.82 toolchain too.

it could be a user issue, cron might be running as a different user then the one you set rustup default toolchain with. Maybe try adding rustup default <toolchain> in the crontab line, just to set it for that user too.

3

Cron runs tasks as root, so you'll need to change the task to run as the desired user instead, e.g. through su - <user> (though that's not technically the most secure way).

Please don't run it as root unless the program needs to be, and even then, you should build as a normal user, then run the executable as root. Building runs build scripts from your dependencies, which aren't sandboxed at all... so running as root gives them full access to your container (which still isn't that bad, but ideally you'd minimize its control anyways).

4

Anyone in the appropriate group can create a cron job that runs under their own account.

5

True, depending on the daemon; but that isn't the usual method of creating cron jobs (at least, IME), and doesn't seem to be what they did here.

6

Different experiences I guess.