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A tool to wait for services and execute command. Useful for Docker containers that depend on slow to start services (like almost everything).

Project description

A tool to wait for services and execute command. Useful for Docker containers that depend on slow to start services (like almost everything).

  • Free software: BSD license

Installation

pip install holdup

Documentation

Usage: holdup [-h] [-t SECONDS] [-T SECONDS] [-i SECONDS] [-n] service [service ...] [-- command [arg [arg ...]]]

Wait for services to be ready and optionally exec command.

Positional arguments:
service
A service to wait for. Supported protocols: “tcp://host:port/”, “path:///path/to/something”, “unix:///path/to/domain.sock”, “eval://expr”, “http://urn”, “http://urn” (status 200 expected). Join protocols with a comma to make holdup exit at the first passing one, eg: tcp://host:1,host:2 or tcp://host:1,tcp://host:2 are equivalent and mean “any that pass”.
command
An optional command to exec.
Optional arguments:
-h, --help show this help message and exit
-t SECONDS, --timeout SECONDS
 Time to wait for services to be ready. Default: 5.0
-T SECONDS, --check-timeout SECONDS
 Time to wait for a single check. Default: 1.0
-i SECONDS, --interval SECONDS
 How often to check. Default: 0.2
-n, --no-abort Ignore failed services. This makes holdup return 0 exit code regardless of services actually responding.

Suggested use

Assuming you always want the container to wait add this in your Dockerfile:

COPY entrypoint.sh /
ENTRYPOINT ["/entrypoint.sh"]
CMD ["/bin/bash"]

Then in entrypoint.sh you could have:

#!/bin/sh
set -eux
urlstrip() { string=${@##*://}; echo ${string%%[\?/]*}; }
exec holdup \
     "tcp://$DJANGO_DATABASE_HOST:$DJANGO_DATABASE_PORT" \
     "tcp://$(urlstrip $CELERY_RESULT_BACKEND)" \
     -- "$@"

The only disadvantage is that you might occasionally need to use docker run --entrypoint='' to avoid running holdup. No biggie.

Development

To run the all tests run:

tox

Note, to combine the coverage data from all the tox environments run:

Windows
set PYTEST_ADDOPTS=--cov-append
tox
Other
PYTEST_ADDOPTS=--cov-append tox

Changelog

1.6.0 (2018-03-22)

  • Added verbose mode (-v or --verbose).
  • Changed default timeout to 60s (from 5s).

1.5.0 (2017-06-07)

  • Added an eval://expression protocol for weird user-defined checks.

1.4.0 (2017-03-27)

  • Added support for HTTP(S) check.

1.3.0 (2017-02-21)

  • Add support for “any” service check (service syntax with comma).

1.2.1 (2016-06-17)

  • Handle situation where internal operations would take more than planned.

1.2.0 (2016-05-25)

  • Added a file check.

1.1.0 (2016-05-06)

  • Removed debug print.
  • Added --interval option for how often to check. No more spinloops.

1.0.0 (2016-04-22)

  • Improved tests.
  • Always log to stderr.

0.1.0 (2016-04-21)

  • First release on PyPI.

Project details


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