A modern Cron replacement that is Docker-friendly
- Free software: MIT license
- "Crontab" is in YAML format;
- Builtin sending of Sentry and Mail outputs when cron jobs fail;
- Flexible configuration: you decide how to determine if a cron job fails or not;
- Designed for running in Docker, Kubernetes, or 12 factor environments:
- Runs in the foreground;
- Logs everything to stdout/stderr [1];
- Option to automatically retry failing cron jobs, with exponential backoff;
- Optional HTTP REST API, to fetch status and start jobs on demand;
- Arbitrary timezone support;
| [1] | Whereas vixie cron only logs to syslog, requiring a syslog daemon to be running in the background or else you don't get logs! |
The project is in beta stage: essential features are complete, and the focus is finding and fixing bugs before the first stable release.
yacron requires Python >= 3.6 (for systems with older Python, use the binary instead). It is advisable to install it in a Python virtual environment, for example:
python3 -m venv yacronenv
. yacronenv/bin/activate
pip install yacronpipx automates creating a virtualenv and installing a python program in the newly created virtualenv. It is as simple as:
pipx install yacronAlternatively, a self-contained binary can be downloaded from github: https://github.com/gjcarneiro/yacron/releases. This binary should work on any Linux 64-bit system post glibc 2.23 (e.g. Ubuntu:16.04). Python is not required on the target system (it is embedded in the executable).
Configuration is in YAML format. To start yacron, give it a configuration file
or directory path as the -c argument. For example:
yacron -c /tmp/my-crontab.yaml
This starts yacron (always in the foreground!), reading
/tmp/my-crontab.yaml as configuration file. If the path is a directory,
any *.yaml or *.yml files inside this directory are taken as
configuration files.
This configuration runs a command every 5 minutes:
jobs:
- name: test-01
command: echo "foobar"
shell: /bin/bash
schedule: "*/5 * * * *"The command can be a string or a list of strings. If command is a string,
yacron runs it through a shell, which is /bin/bash in the above example, but
is /bin/sh by default.
If the command is a list of strings, the command is executed directly, without a shell. The ARGV of the command to execute is extracted directly from the configuration:
jobs:
- name: test-01
command:
- echo
- foobar
schedule: "*/5 * * * *"The schedule option can be a string in a crontab format specified by https://github.com/josiahcarlson/parse-crontab (this module is used by yacron). Additionally @reboot can be included , which will only run the job when yacron is initially executed. Further schedule can be an object with properties. The following configuration runs a command every 5 minutes, but only on the specific date 2017-07-19, and doesn't run it in any other date:
jobs:
- name: test-01
command: echo "foobar"
schedule:
minute: "*/5"
dayOfMonth: 19
month: 7
year: 2017
dayOfWeek: "*"Important: by default all time is interpreted to be in UTC, but you can
request to use local time instead. For instance, the cron job below runs
every day at 19h27 local time because of the utc: false option:
jobs:
- name: test-01
command: echo "hello"
schedule: "27 19 * * *"
utc: false
captureStdout: trueSince Yacron version 0.11, you can also request that the schedule be
interpreted in an arbitrary timezone, using the timezone attribute:
jobs:
- name: test-01
command: echo "hello"
schedule: "27 19 * * *"
timezone: America/Los_Angeles
captureStdout: trueYou can ask for environment variables to be defined for command execution:
jobs:
- name: test-01
command: echo "foobar"
shell: /bin/bash
schedule: "*/5 * * * *"
environment:
- key: PATH
value: /bin:/usr/binYou can also provide an environment file to define environments for command execution:
jobs:
- name: test-01
command: echo "foobar"
shell: /bin/bash
schedule: "*/5 * * * *"
env_file: .envThe env file must be a list of KEY=VALUE pairs. Empty lines and lines starting with # will be ignored.
Variables declared in the environment option will override those found in the env_file.
There can be a special defaults section in the config. Any attributes
defined in this section provide default values for cron jobs to inherit.
Although cron jobs can still override the defaults, as needed:
defaults:
environment:
- key: PATH
value: /bin:/usr/bin
shell: /bin/bash
utc: false
jobs:
- name: test-01
command: echo "foobar" # runs with /bin/bash as shell
schedule: "*/5 * * * *"
- name: test-02 # runs with /bin/sh as shell
command: echo "zbr"
shell: /bin/sh
schedule: "*/5 * * * *"Note: if the configuration option is a directory and there are multiple configuration files in that directory, then the defaults section in each configuration file provides default options only for cron jobs inside that same file; the defaults have no effect beyond any individual YAML file.
Yacron has builtin support for reporting jobs failure (more on that below) by email, Sentry and shell command (additional reporting methods might be added in the future):
- name: test-01
command: |
echo "hello" 1>&2
sleep 1
exit 10
schedule:
minute: "*/2"
captureStderr: true
onFailure:
report:
sentry:
dsn:
value: example
# Alternatively:
# fromFile: /etc/secrets/my-secret-dsn
# fromEnvVar: SENTRY_DSN
fingerprint: # optional, since yacron 0.6
- yacron
- "{{ environment.HOSTNAME }}"
- "{{ name }}"
extra:
foo: bar
zbr: 123
level: warning
environment: production
mail:
from: [email protected]
to: [email protected]
smtpHost: 127.0.0.1
# optional fields:
username: "username1" # set username and password to enable login
password:
value: example
# Alternatively:
# fromFile: /etc/secrets/my-secret-password
# fromEnvVar: MAIL_PASSWORD
tls: false # set to true to enable TLS
starttls: false # set to true to enable StartTLS
shell:
shell: /bin/bash
command: ...Here, the onFailure object indicates that what to do when a job failure
is detected. In this case we ask for it to be reported both to sentry and by
sending an email.
The captureStderr: true part instructs yacron to capture output from the the
program's standard error, so that it can be included in the report. We could
also turn on standard output capturing via the captureStdout: true option.
By default, yacron captures only standard error. If a cron job's standard error
or standard output capturing is not enabled, these streams will simply write to
the same standard output and standard error as yacron itself.
Both stdout and stderr stream lines are by default prefixed with
[{job_name} {stream_name}], i.e. [test-01 stdout], if for any reason you
need to change this, provide the option streamPrefix (new in version 0.16)
with your own custom string.
- name: test-01
command: echo "hello world"
schedule:
minute: "*/2"
captureStdout: true
streamPrefix: "[{job_name} job]"In some cases, for instance when you're logging JSON objects you might want to completely get rid of the prefix altogether:
- name: test-01
command: echo "hello world"
schedule:
minute: "*/2"
captureStdout: true
streamPrefix: ""It is possible also to report job success, as well as failure, via the
onSuccess option.
- name: test-01
command: echo "hello world"
schedule:
minute: "*/2"
captureStdout: true
onSuccess:
report:
mail:
from: [email protected]
to: [email protected]
smtpHost: 127.0.0.1Since yacron 0.5, it is possible to customise the format of the report. For
mail reporting, the option subject indicates what is the subject of the
email, while body formats the email body. For Sentry reporting, there is
only body. In all cases, the values of those options are strings that are
processed by the jinja2 templating engine. The following variables are
available in templating:
- name(str): name of the cron job
- success(bool): whether or not the cron job succeeded
- stdout(str): standard output of the process
- stderr(str): standard error of the process
- exit_code(int): process exit code
- command(str): cron job command
- shell(str): cron job shell
- environment(dict): subprocess environment variables
Example:
- name: test-01
command: |
echo "hello" 1>&2
sleep 1
exit 10
schedule:
minute: "*/2"
captureStderr: true
onFailure:
report:
mail:
from: [email protected]
to: [email protected]
smtpHost: 127.0.0.1
subject: Cron job '{{name}}' {% if success %}completed{% else %}failed{% endif %}
body: |
{{stderr}}
(exit code: {{exit_code}})The shell reporter (since yacron 0.13) executes a user given shell command in the specified shell. It passes all environment variables from the python executable and specifies some additional ones to inform about the state of the job:
- YACRON_FAIL_REASON (str)
- YACRON_FAILED ("1" or "0")
- YACRON_JOB_NAME (str)
- YACRON_JOB_COMMAND (str)
- YACRON_JOB_SCHEDULE (str)
- YACRON_RETCODE (str)
- YACRON_STDERR (str)
- YACRON_STDOUT (str)
A simple example configuration:
- name: test-01
command: echo "foobar" && exit 123
shell: /bin/bash
schedule: "* * * * *"
onFailure:
report:
shell:
shell: /bin/bash
command: echo "Error code $YACRON_RETCODE"Since yacron 0.15, it is possible to send emails formatted as html, by adding
the html: true property. For example, here the standard output of a shell
command is captured and interpreted as html and placed in the email message:
- name: test-01
command: echo "hello <b>world</b>"
schedule: "@reboot"
captureStdout: true
onSuccess:
report:
mail:
from: [email protected]
to: [email protected], [email protected]
html: true
smtpHost: 127.0.0.1
smtpPort: 1025
subject: This is a cron job with html bodyYacron has builtin support for writing job metrics to Statsd:
jobs:
- name: test01
command: echo "hello"
schedule: "* * * * *"
statsd:
host: my-statsd.example.com
port: 8125
prefix: my.cron.jobs.prefix.test01With this config Yacron will write the following metrics over UDP
to the Statsd listening on my-statsd.example.com:8125:
my.cron.jobs.prefix.test01.start:1|g # this one is sent when the job starts my.cron.jobs.prefix.test01.stop:1|g # the rest are sent when the job stops my.cron.jobs.prefix.test01.success:1|g my.cron.jobs.prefix.test01.duration:3|ms|@0.1
By default, yacron considers that a job has failed if either the process returns a non-zero code or if it generates output to standard error (and standard error capturing is enabled, of course).
You can instruct yacron how to determine if a job has failed or not via the
failsWhen option:
failsWhen:
producesStdout: false
producesStderr: true
nonzeroReturn: true
always: false- producesStdout
- If true, any captured standard output causes yacron to consider the job as failed. This is false by default.
- producesStderr
- If true, any captured standard error causes yacron to consider the job as failed. This is true by default.
- nonzeroReturn
- If true, if the job process returns a code other than zero causes yacron to consider the job as failed. This is true by default.
- always
- If true, if the job process exits that causes yacron to consider the job as failed. This is false by default.
It is possible to instruct yacron to retry failing cron jobs by adding a
retry option inside onFailure:
- name: test-01
command: |
echo "hello" 1>&2
sleep 1
exit 10
schedule:
minute: "*/10"
captureStderr: true
onFailure:
report:
mail:
from: [email protected]
to: [email protected]
smtpHost: 127.0.0.1
retry:
maximumRetries: 10
initialDelay: 1
maximumDelay: 30
backoffMultiplier: 2The above settings tell yacron to retry the job up to 10 times, with the delay between retries defined by an exponential backoff process: initially 1 second, doubling for every retry up to a maximum of 30 seconds. A value of -1 for maximumRetries will mean yacron will keep retrying forever, this is mostly useful with a schedule of "@reboot" to restart a long running process when it has failed.
If the cron job is expected to fail sometimes, you may wish to report only in
the case the cron job ultimately fails after all retries and we give up on it.
For that situation, you can use the onPermanentFailure option:
- name: test-01
command: |
echo "hello" 1>&2
sleep 1
exit 10
schedule:
minute: "*/10"
captureStderr: true
onFailure:
retry:
maximumRetries: 10
initialDelay: 1
maximumDelay: 30
backoffMultiplier: 2
onPermanentFailure:
report:
mail:
from: [email protected]
to: [email protected]
smtpHost: 127.0.0.1Sometimes it may happen that a cron job takes so long to execute that when the moment its next scheduled execution is reached a previous instance may still be running. How yacron handles this situation is controlled by the option concurrencyPolicy, which takes one of the following values:
- Allow
- allows concurrently running jobs (default)
- Forbid
- forbids concurrent runs, skipping next run if previous hasn’t finished yet
- Replace
- cancels currently running job and replaces it with a new one
(new in version 0.4)
If you have a cron job that may possibly hang sometimes, you can instruct yacron
to terminate the process after N seconds if it's still running by then, via the
executionTimeout option. For example, the following cron job takes 2
seconds to complete, yacron will terminate it after 1 second:
- name: test-03
command: |
echo "starting..."
sleep 2
echo "all done."
schedule:
minute: "*"
captureStderr: true
executionTimeout: 1 # in secondsWhen terminating a job, it is always a good idea to give that job process some time to terminate properly. For example, it may have opened a file, and even if you tell it to shutdown, the process may need a few seconds to flush buffers and avoid losing data.
On the other hand, there are times when programs are buggy and simply get stuck,
refusing to terminate nicely no matter what. For this reason, yacron always
checks if a process exited some time after being asked to do so. If it hasn't,
it tries to forcefully kill the process. The option killTimeout option
indicates how many seconds to wait for the process to gracefully terminate
before killing it more forcefully. In Unix systems, we first send a SIGTERM,
but if the process doesn't exit after killTimeout seconds (30 by default)
then we send SIGKILL. For example, this cron job ignores SIGTERM, and so yacron
will send it a SIGKILL after half a second:
- name: test-03
command: |
trap "echo '(ignoring SIGTERM)'" TERM
echo "starting..."
sleep 10
echo "all done."
schedule:
minute: "*"
captureStderr: true
executionTimeout: 1
killTimeout: 0.5(new in version 0.11)
You can request that Yacron change to another user and/or group for a specific
cron job. The field user indicates the user (uid or userame) under which
the subprocess must be executed. The field group (gid or group name)
indicates the group id. If only user is given, the group defaults to the
main group of that user. Example:
- name: test-03
command: id
schedule:
minute: "*"
captureStderr: true
user: www-dataNaturally, yacron must be running as root in order to have permissions to change to another user.
(new in version 0.10)
If you wish to remotely control yacron, you can optionally enable an HTTP REST interface, with the following configuration (example):
web:
listen:
- http://127.0.0.1:8080
- unix:///tmp/yacron.sockNow you have the following options to control it (using HTTPie as example):
$ http get http://127.0.0.1:8080/version
HTTP/1.1 200 OK
Content-Length: 22
Content-Type: text/plain; charset=utf-8
Date: Sun, 03 Nov 2019 19:48:15 GMT
Server: Python/3.7 aiohttp/3.6.2
0.10.0b3.dev7+g45bc4ce$ http get http://127.0.0.1:8080/status
HTTP/1.1 200 OK
Content-Length: 104
Content-Type: text/plain; charset=utf-8
Date: Sun, 03 Nov 2019 19:44:45 GMT
Server: Python/3.7 aiohttp/3.6.2
test-01: scheduled (in 14 seconds)
test-02: scheduled (in 74 seconds)
test-03: scheduled (in 14 seconds)You may also get status info in json format:
$ http get http://127.0.0.1:8080/status Accept:application/json
HTTP/1.1 200 OK
Content-Length: 206
Content-Type: application/json; charset=utf-8
Date: Sun, 03 Nov 2019 19:45:53 GMT
Server: Python/3.7 aiohttp/3.6.2
[
{
"job": "test-01",
"scheduled_in": 6.16588,
"status": "scheduled"
},
{
"job": "test-02",
"scheduled_in": 6.165787,
"status": "scheduled"
},
{
"job": "test-03",
"scheduled_in": 6.165757,
"status": "scheduled"
}
]Sometimes it's useful to start a cron job right now, even if it's not scheduled to run yet, for example for testing:
$ http post http://127.0.0.1:8080/jobs/test-02/start
HTTP/1.1 200 OK
Content-Length: 0
Content-Type: application/octet-stream
Date: Sun, 03 Nov 2019 19:50:20 GMT
Server: Python/3.7 aiohttp/3.6.2(new in version 0.13)
You may have a use case where it's convenient to have multiple config files, and choose at runtime which one to use. In that case, it might be useful if you can put common definitions (such as defaults for reporting, shell, etc.) in a separate file, that is included by the other files.
To support this use case, it is possible to ask one config file to include
another one, via the include directive. It takes a list of file names:
those files will be parsed as configuration and merged in with this file.
Example, your main config file could be:
include:
- _inc.yaml
jobs:
- name: my job
...And your included _inc.yaml file could contain some useful defaults:
defaults:
shell: /bin/bash
onPermanentFailure:
report:
sentry:
...It's possible to provide a custom logging configuration, via the logging
configuration section. For example, the following configuration displays log lines with
an embedded timestamp for each message.
logging:
# In the format of:
# https://docs.python.org/3/library/logging.config.html#dictionary-schema-details
version: 1
disable_existing_loggers: false
formatters:
simple:
format: '%(asctime)s [%(processName)s/%(threadName)s] %(levelname)s (%(name)s): %(message)s'
datefmt: '%Y-%m-%d %H:%M:%S'
handlers:
console:
class: logging.StreamHandler
level: DEBUG
formatter: simple
stream: ext://sys.stdout
root:
level: INFO
handlers:
- console(new in yacron 0.18)
It is possible to disable a specific cron job by adding a enabled: false option. Jobs with enabled: false will simply be skipped, as if they aren't there, apart from validating the configuration.
jobs:
- name: test-01
enabled: false # this cron job will not run until you change this to `true`
command: echo "foobar"
shell: /bin/bash
schedule: "* * * * *"
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