📚 wait-for - Awesome Go Library for Software Packages
Wait for something to happen (from the command line) before continuing. Easy orchestration of Docker services and other things.
Detailed Description of wait-for
wait-for
This is a CLI tool that waits for an event before continuing. Simples. But it does it cross platform and as a single dependency that can be downloaded into your container or environment.
Typically, you would use this to wait on another resource (such as an HTTP resource) to become available before continuing - or timeout and exit with an error.
At the moment, you can wait for a few different kinds of thing. They are:
- HTTP or HTTPS success response or any expected response following regular expressions
- TCP or GRPC connection
- DNS IP resolve address change
Installing wait-for
Using the go
command:
go install github.com/dnnrly/wait-for/cmd/wait-for@latest
If you don't have Go installed (in a Docker container, for example) then you can take advantage of the pre-built versions. Check out the releases and check out the links for direct downloads. You can download and unpack a release like so:
wget https://github.com/dnnrly/wait-for/releases/download/v0.0.5/wait-for_0.0.5_linux_386.tar.gz
gunzip wait-for_0.0.5_linux_386.tar.gz
tar -xfv wait-for_0.0.5_linux_386.tar
In your Dockerfile, you can do this:
ADD https://github.com/dnnrly/wait-for/releases/download/v0.0.1/wait-for_0.0.5_linux_386.tar.gz wait-for.tar.gz
RUN gunzip wait-for.tar.gz && tar -xf wait-for.tar
Feel free to choose from any of the other releases though.
Using wait-for
Waiting for arbitrary HTTP services
$ wait-for http://your-service-here:8080/health https://another-service/
Waiting for HTTP services with expected response status
$ wait-for -status=[0-2]{3} http://your-service-here:8080/health
Waiting for gRPC services
$ wait-for grpc-server:8092 other-grpc-server:9091
Waiting for DNS changes
$ wait-for dns:google.com
This will wait for the list of IP addresses bound to that DNS name to be updated, regardless of order. You can use this to wait for a DNS update such as failover or other similar operations.
Preconfiguring services to connect to
$ wait-for preconfigured-service
By default, wait-for
will look for a file in the current directory called
.wait-for.yml
. In this, you can define the names of services that you would
like to wait on.
wait-for:
preconfigured-service:
type: http
target: http://the-service:8080/health?reload=true
interval: 5s
timeout: 60s
http-client-timeout: 3s
another-service:
type: http
target: https://another-one
grpcService:
type: grpc
target: localhost:9092
snmp-service:
type: tcp
target: snmp-trap-dns:514
dns-thing:
type: dns
target: your.r53-entry.com
Using wait-for
in Docker Compose
You can use wait-for
to do some of the orchestration for you in your compose file. A good example
would be something like this:
version: '3'
services:
web:
build: .
ports:
- "8080"
command: sh -c 'wait-for tcp:db:5432 && ./your-api
depends_on:
- db
db:
image: "postgres:13-alpine"
command: "-c log_statement=all"
environment:
POSTGRES_DB: weallvote-api
POSTGRES_USER: ${POSTGRES_USER:-postgres}
POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-postgres}
Developing wait-for
Building the tool
To build the tool so that you can run it locally, you can use the following command.
$ make build
Unit tests
You can run the tests as the build system would, using the following command:
$ make test
You can also run the Go tests in the 'usual' way with the following command:
$ go test ./...
Acceptance tests
There is a suite of GoDog tests that check that the built tooling works as expected.
$ make acceptance-test
Depending on how your system is set up, it might not be possible for you to open up the necessary ports to run the acceptance tests. To get around this you can run those same tests in Docker
$ make acceptance-test-docker