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Create a `golock` program this is based on the following: https://github.com/kvz/cronlock This is because the above hasn't been maintained for many years, and I need something that does the equivalent but to be able to talk to Redis servers that enforce TLS encryption. Add `util.GenEnv()`, `util.GetEnvBool()`, and `util.GetEnvInt()` functions to get values from the environment variables and return them in a certain type. If the environment variables are not set, then the default value to be returned is passed to these functions. Add a `util.Run()` function to execute a command with an optional timeout so that it will be killed if it exceeds that runtime.
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| * @jim-barber-he |
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| # My Go repository | ||
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| ## Introduction | ||
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| This repository was created for me to use as I'm learning to write Go. | ||
| I decided that the best way for me to learn it was to write some utilities that will be useful for me in my line of work. | ||
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| ## Utilities | ||
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| The utilities in this repository are: | ||
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| - [golock](golock/) Creates locks in a [Redis](https://redis.io/) server to coordinate running a command on distributed servers. | ||
| - [kubectl-n](kubectl-plugins/kubectl-n) A [kubectl](https://kubernetes.io/docs/reference/kubectl/) plugin that is an alternate | ||
| version of `kubectl get nodes`. | ||
| - [kubectl-p](kubectl-plugins/kubectl-p) A [kubectl](https://kubernetes.io/docs/reference/kubectl/) plugin that is an alternate | ||
| version of `kubectl get pods`. | ||
| - [ssm](ssm/) A tool for managing AWS SSM parameters. | ||
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| ## Go Libraries | ||
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| The following libraries in this repository were written to implement the utilities above. | ||
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| - [aws](aws/) Implements functions to interact with Amazon Web Services. | ||
| - [k8s](k8s/) Implements functions to interact with Kubernetes clusters. | ||
| - [texttable](texttable/) Implements functions for handling outputting a text based table. | ||
| - [util](util/) Implements various utility functions. |
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| # Things to do | ||
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| * Add README.md | ||
| * Make repo public. | ||
| * Add JSON output for the `get` and `list` commands for `ssm`. | ||
| * Improve tests and add tests for the AWS stuff once I work out how to mock them. | ||
| * `ssm` command to handle advanced parameters; policies; intelligent tiering. | ||
| * Add `--no-value` parameter to `ssm list` to return just the names of parameters. | ||
| * `ssm` command to handle advanced parameters; policies; and intelligent tiering. | ||
| * Implement `ssm copy` command. | ||
| * Command line completion for the --namespace option in k8s commands. | ||
| * Improve / add tests and add tests for the AWS stuff once I work out how to mock them. |
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| ARCH := $(shell uname -s | tr '[A-Z]' '[a-z]') | ||
| BINARY_NAME=golock | ||
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| .PHONY: all build clean install lint run vet | ||
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| all: vet lint build install | ||
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| build: | ||
| GOARCH=amd64 GOOS=darwin go build -o ${BINARY_NAME}-darwin -race main.go | ||
| GOARCH=amd64 GOOS=linux go build -o ${BINARY_NAME}-linux -race main.go | ||
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| clean: | ||
| go clean | ||
| rm -f ${BINARY_NAME}-darwin ${BINARY_NAME}-linux | ||
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| install: | ||
| go install -ldflags='-s' | ||
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| lint: | ||
| golangci-lint run | ||
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| lintall: | ||
| golangci-lint run --enable-all | ||
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| run: build | ||
| ./${BINARY_NAME}-${ARCH} | ||
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| vet: | ||
| go vet |
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| # golock | ||
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| ## Introduction | ||
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| golock uses a central Redis server to globally coordinate the running of a job across a distributed system. | ||
| This is useful where you only want a job to run once, but want to schedule it on multiple servers for redundancy. | ||
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| Also by only allowing one job to run at a time, it can stop jobs that are scheduled to frequently run, from overlapping | ||
| themselves. | ||
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| It is a cronlock replacement, based on https://github.com/kvz/cronlock | ||
| It creates locks with the same names as cronlock does, and uses many of the same environment variables. | ||
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| The purpose of writing golock is because cronlock does not support Redis servers where TLS is enforced. | ||
| And also it is an exercise in me learning Golang. | ||
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| ## Options. | ||
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| - `CRONLOCK_HOST` the Redis hostname. default: `localhost` | ||
| - `CRONLOCK_PORT` the Redis port. default: `6379` | ||
| - `CRONLOCK_AUTH` the Redis auth password. default: Not present | ||
| - `CRONLOCK_DB` the Redis database. default: `0` | ||
| - `CRONLOCK_REDIS_TIMEOUT` the length of time to wait for a response from Redis before considering it in an errored state. | ||
| This ensures that if the Redis connection goes away that we don't wait forever waiting for a response. default: `30` | ||
| - `CRONLOCK_GRACE` determines how many seconds a lock should at least persist. | ||
| Prevents fast running jobs scheduled on multiple servers with some clock drift, from executing multiple times. | ||
| - `CRONLOCK_RELEASE` determines how long a lock can persist at most. | ||
| Acts as a failsafe so there can be no locks that persist forever in case of failure. default is a day: `86400` | ||
| - `CRONLOCK_RECONNECT_ATTEMPTS` the number of times to try to reconnect before erroring. | ||
| If the Redis connection is closed, attempt to reconnect upto this amount of times. default: `5` | ||
| - `CRONLOCK_RECONNECT_BACKOFF` the length of time to increase the wait between reconnects. | ||
| Acts as a failsafe to allow Redis to be started before trying to reconnect. | ||
| Set to 0 to retry the connection immediately. default: `5` | ||
| - `CRONLOCK_KEY` a unique key for this command in the global Redis server. default: an md5 hash of golock's arguments. | ||
| - `CRONLOCK_PREFIX` Redis key prefix used by all keys. default: `cronlock` | ||
| - `CRONLOCK_VERBOSE` set to `yes` to print debug messages. default: `no` | ||
| - `CRONLOCK_TIMEOUT` how long the command can run before it gets issued a `kill -9`. default: `0`; no timeout | ||
| - `CRONLOCK_TLS` use TLS to connect to Redis. default `false` | ||
| - `CRONLOCK_TLS_SKIP_VERIFY` donot verify TLS certificates when using TLS connections. default `false`; | ||
| certificates are verified. | ||
| - `CRONLOCK_RESET` removes the lock and exits immediately. Needs to golock arguments passed in order to remove the right lock. | ||
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| ## Exit Codes | ||
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| - = `200` Success (delete succeeded or lock not acquired, but normal execution) | ||
| - = `201` Failure (cronlock error) | ||
| - = `202` Failure (cronlock timeout) | ||
| - < `200` Success (acquired lock, executed your command), passes the exit code of your command | ||
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| ## Examples | ||
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| ### Single server | ||
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| ``` | ||
| * * * * * golock command.sh | ||
| ``` | ||
| The above crontab entry launches `command.sh` every minute. | ||
| If the previous `command.sh` has not finished yet, another is not started. | ||
| This works on one server since the default `CRONLOCK_HOST` of `localhost` is used. | ||
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| ### Distributed | ||
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| ``` | ||
| 00 08 * * * CRONLOCK_HOST=redis.example.com golock command.sh | ||
| ``` | ||
| In this configuration, a central Redis server is used to track the locking for `command.sh`. | ||
| If this crontab entry was on many servers, just one instance of `command.sh` would be run each morning. | ||
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| ### Lock commands that have different arguments | ||
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| By default golock uses your command and its arguments to make a unique identifier by which the global lock is acquired. | ||
| However if you want to run `ls -al` or `ls -a`, but just one instance of either, you'll need to provide your own key: | ||
| ``` | ||
| # One of two will be executed because they share the same KEY | ||
| * * * * * CRONLOCK_KEY="ls" golock ls -al | ||
| * * * * * CRONLOCK_KEY="ls" golock ls -a | ||
| ``` | ||
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| ### Per application | ||
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| If you use the same command and Redis server for multiple applications and you need them to run without impacting each other, | ||
| use the `CRONLOCK_PREFIX`: | ||
| ``` | ||
| # Crontab for app1 | ||
| * * * * * CRONLOCK_PREFIX="lock.app1." cronlock command.sh | ||
| ``` | ||
| ``` | ||
| # Crontab for app2 | ||
| * * * * * CRONLOCK_PREFIX="lock.app2." cronlock command.sh | ||
| ``` | ||
| Now `command.sh` will be able to run for each application at the same time, because even though `command.sh` will produce the same | ||
| md5 hash for both, the key's prefix makes it unique. | ||
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| ## Local Redis for testing | ||
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| A quick way of getting a Redis server locally if you have Docker available is to run: | ||
| ```shell | ||
| docker run --rm -it -p 6379:6379 redis:latest | ||
| ``` |
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