readiness.sh

Overview

`readiness.sh` is a lightweight Bash script designed to perform a readiness check for a service named **midgard** running locally on port 8080. It verifies whether the service's health endpoint reports that the system is "in sync," indicating readiness to handle requests. The script is intended to be used as a readiness probe in container orchestration platforms (like Kubernetes), or as a simple health check utility in deployment pipelines or monitoring systems.

Detailed Explanation

Script Purpose

• Query the health status of the midgard service via HTTP.

• Parse the response to check if the service is "in sync".

• Exit with status code 0 if ready, 1 otherwise.

Script Breakdown

#!/bin/bash

• Specifies the script interpreter as Bash.

HEALTH=$(curl -sf http://localhost:8080/v2/health) || exit 1

• Uses curl to silently (-s) and fail silently on errors (-f) to request the /v2/health endpoint on localhost:8080.

• Assigns the JSON response to the variable HEALTH.

• If the request fails (e.g., server not responding), the script immediately exits with status code 1 (failure).

IN_SYNC=$(echo $HEALTH | jq -r '.inSync')

• Uses jq (a command-line JSON processor) to extract the value of the inSync field from the JSON response.

• The -r option outputs the raw string value.

• Assumes the JSON response contains a boolean property inSync.

if [[ $IN_SYNC == true ]]; then
  echo "midgard is synced"
  exit 0
fi

• Checks if the extracted inSync value is true.

• If yes, prints a success message and exits with code 0 (success).

echo "midgard is still syncing"
exit 1

• If inSync is not true, prints a message indicating the service is still syncing and exits with code 1 (failure).

Parameters and Environment

• No parameters: The script does not accept any command-line arguments.

• Dependencies:

  • curl: to perform HTTP requests.

  • jq: to parse JSON responses.

• Assumptions:

  • The midgard service is accessible at http://localhost:8080/v2/health.

  • The health endpoint returns a JSON object with an inSync boolean field.

Usage Example

Run the script as a standalone command:

./readiness.sh

Possible outputs and exit codes:

This makes the script suitable for integration as a readiness probe in orchestration systems:

readinessProbe:
  exec:
    command:
    - /bin/bash
    - /path/to/readiness.sh
  initialDelaySeconds: 10
  periodSeconds: 5

Implementation Details / Algorithms

• The script relies on a simple HTTP GET request and JSON parsing.

• It uses a fail-fast approach: if the HTTP request fails, it immediately exits.

• The decision logic is a straightforward conditional check on the inSync JSON value.

• No loops or complex algorithms are used, ensuring minimal runtime and resource usage.

Interaction With Other System Components

• Midgard Service: The script interacts directly with the midgard service by querying its health endpoint.

• Container Orchestrators / Monitoring Tools: Can be invoked by Kubernetes readiness probes or external monitoring scripts to determine if midgard is ready to serve traffic.

• System Utilities: Depends on curl and jq installed in the environment.

The script acts as a bridge between midgard's internal health status and external systems that need to make decisions about routing traffic or triggering alerts.

Flowchart Representing Script Workflow

flowchart TD
    A[Start] --> B{Run curl request<br>to /v2/health}
    B -- Success --> C[Parse JSON with jq<br>extract 'inSync']
    B -- Failure --> G[Exit 1: Health check failed]
    C --> D{Is inSync == true?}
    D -- Yes --> E[Print "midgard is synced"<br>Exit 0]
    D -- No --> F[Print "midgard is still syncing"<br>Exit 1]

Summary

`readiness.sh` is a simple, effective readiness probe script for the midgard service. It performs an HTTP health check, parses JSON output to verify service synchronization status, and returns appropriate exit codes to signal readiness. Its minimal dependencies and clear logic make it ideal for integration into automated deployment and monitoring pipelines.