eb

eb is a small command-line application that tries its given command-line arguments with an exponentially-increasing timeout as non-zero status codes are returned. You might use this when, for example, you have a program that exits if something fails.

eb only exits once a status code of 0 has been returned.

You can use eb like watch:

$ eb -- nc -z 192.0.2.42 53

Installing it

You can install eb via

$ cargo install eb

Features

We currently support these features:

• simple_logger enables the simple_logger logger.

There are no features enabled by default.

The algorithm

In the above console input, eb will watch the command and keep track of how long it takes to fail. Upon the first failure, a "slot time" is set to the time it took for the command to fail.

In each instance, after n failures, a random number of slot times between 0 and 2^n - 1 is chosen, and these slot times are delayed through. So, after the first failure, eb will either wait 0 or 1 slot times; after the second failure this number increases to between 0 and 3. The exponent n is clamped to be within the range 0 and MAX_N where MAX_N is some predefined number; in our case this is 10. In practice, this means that after 10 collisions, the possible upper bound on delay does not increase. Because commands take a variable amount of time to complete, the slot time is adjusted to be the average of all execution times. The delay will start very quickly after the command fails.

Because of the way the algorithm works, it is recommended to use eb in situations where the given command will fail quickly. This will result in a proportionally small maximum delay time.

License

eb: A command executor exercising exponential backoff
Copyright (C) 2019 Kristofer J. Rye

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.