host_check/README.md

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# Purpose
This Go binary conducts network diagnostics on a set of hostnames, ideal for verifying connectivity to dependent services or containers.
## Usage
1. **Build:**
Execute the build script:
```bash
./build.sh
```
2. **Set Environment Variables:**
* **HOST_CHECK_HOSTNAMES:** Comma-separated list of hostnames to check (e.g., `database,redis-server,api.example.com`).
* **HOST_CHECK_FAIL_ON_ERROR** (optional): Set to "true" to halt execution immediately if a ping to any hostname fails.
* **HOST_CHECK_COMMAND** (optional): Command to execute if all hosts are successfully pinged (e.g., `entrypoint.sh` to run a script on each host).
* **HOST_CHECK_ERROR_COMMAND** (optional): Command to execute if a ping fails, useful for automated error handling (e.g., `go-glitch report-error <hostname> 'Ping failed'`).
3. **Run:**
Start the host check:
```bash
./host_check
```
## Output
For each hostname, the output includes:
* **DNS Resolution:** Indicates success or failure, displaying resolved IPs if successful.
* **Ping:** Indicates success or failure, including ping statistics if successful.
* **Custom Script:** Displays the output of the `HOST_CHECK_COMMAND` script, if executed.
* **Error Reporting:** Displays the output of the `HOST_CHECK_ERROR_COMMAND`, if a ping failure occurs.
## Example
To verify connectivity to "db-container" and "webserver", execute the `entrypoint.sh` script, and handle errors via go-glitch:
```bash
export HOST_CHECK_HOSTNAMES="db-container,webserver"
export HOST_CHECK_COMMAND="entrypoint.sh"
export HOST_CHECK_ERROR_COMMAND="go-glitch report-error <hostname> 'Ping failed'"
./host_check
```