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wait-for

A Layer 7 (Application) aware way to detect when services are fully initialized.

Overview

Reliable integration and service tests require accurately detecting when services are fully initialized before beginning test execution. While solutions like wait-for-it.sh can reliably detect when services are listening and able to receive connections many services require a deeper check. wait-for provides application specific detection for service initialization.

alt text

wait-for is useful in integration and service tests, where the test suite expects all services to be initialized before execution. For many applications a TCP (level 4) initialization check isn't sufficient. Services begin listening on sockets before they are fully initialized and able to begin performing work.

For example consider Hashicorp's Vault. Upon startup it quickly begins to listen so a wait-for-it.sh check would pass. But true application level initialization can lag behind seconds after it begins to listen, and necessitates an application level check:

EXPECTED="{\"initialized\":true,\"sealed\":false,\"standby\":false}"
VAULT_STATUS=$(curl -s http://127.0.0.1:8200/v1/sys/health | jq -r -j -S -c '{initialized, sealed, standby}')
until [ "$VAULT_STATUS" = "$EXPECTED" ]; do
     VAULT_STATUS=$(curl -s http://127.0.0.1:8200/v1/sys/health | jq -r -j -S -c '{initialized, sealed, standby}')
     echo "$SCRIPT polling vault status, expected: $EXPECTED received: $VAULT_STATUS"
     sleep 1
done

wait-for contains logic necessary to perform these application level checks. Additionally, it offers the same functionality as wait-for-it.sh by providing TCP/UDP based checks. wait-for also supports generic HTTP checks.

Usage

$ ./wait-for
NAME:
   wait-for - wait for a service to become available

USAGE:
   wait-for [global options] command [command options] [arguments...]

VERSION:
   0.0.0

COMMANDS:
     http
     mysql
     postgres
     help, h   Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --timeout value, -t value          duration to wait until marking as failure and returning (default: 5m0s)
   --poll-interval value, --pi value  interval (default: 100ms)
   --help, -h                         show help
   --version, -v                      print the version

Quickstart HTTP

Success

```
$ ./wait-for http --url=http://google.com/
{"level":"info","msg":"polling","time":"2018-08-26T00:50:39Z"}
{"level":"debug","module":"poller.HTTP","msg":"http_response","status_code":200,"time":"2018-08-26T00:50:40Z"}

$ echo $?
0
```

Timeout Reached

```
$ ./wait-for -t 500ms http --url=http://www.google.com/1/2
{"level":"info","msg":"polling","time":"2018-08-28T12:43:30Z"}
{"level":"debug","module":"poller.HTTP","msg":"http_response","status_code":404,"time":"2018-08-28T12:43:30Z"}
{"level":"info","msg":"polling","time":"2018-08-28T12:43:30Z"}
{"level":"debug","module":"poller.HTTP","msg":"http_response","status_code":404,"time":"2018-08-28T12:43:30Z"}
{"level":"info","msg":"polling","time":"2018-08-28T12:43:30Z"}
{"level":"debug","module":"poller.HTTP","msg":"http_response","status_code":404,"time":"2018-08-28T12:43:31Z"}
{"level":"info","msg":"polling","time":"2018-08-28T12:43:31Z"}
{"level":"debug","module":"poller.HTTP","msg":"http_response","status_code":404,"time":"2018-08-28T12:43:31Z"}
{"level":"info","msg":"polling","time":"2018-08-28T12:43:31Z"}
{"level":"debug","module":"poller.HTTP","msg":"http_response","status_code":404,"time":"2018-08-28T12:43:31Z"}
{"level":"info","msg":"polling","time":"2018-08-28T12:43:31Z"}
{"level":"debug","module":"poller.HTTP","msg":"http_response","status_code":404,"time":"2018-08-28T12:43:31Z"}
{"level":"info","msg":"timeout_reached","time":"2018-08-28T12:43:31Z"}
{"level":"fatal","msg":"timeout reached: 500ms","time":"2018-08-28T12:43:31Z"}

$ echo $?
1
```

Documentation Contents

Protocols

Applications