bm-rotate.sh

Overview

bm-rotate.sh is a bash script designed to send a SIGHUP (signal hang up) to a running Docker container process associated with the "block_manager" service. Its primary functionality is to identify the container by a specific Docker Compose service label, retrieve the process ID (PID) of the container's main process, check if the process is active, and then send the SIGHUP signal to prompt the container to reload its configuration or perform any other signal-defined behavior. The script provides timestamped log messages indicating success or failure of each operation.

Script Workflow and Functionality

The script performs the following key steps:

1. Locate the Block Manager container
   Uses docker ps with a filter on the label com.docker.compose.service=block_manager to find the container ID of the relevant container. This label is typically assigned by Docker Compose to containers based on the service name.

2. Check if the container exists
   The script verifies whether container_id is non-empty. If empty, it logs that the container was not found.

3. Retrieve the container's main process ID (PID)
   Uses docker inspect with a Go template to extract the PID of the container's init process on the host system.

4. Check if the process is running
   Uses ps -e and grep to verify if the process with the retrieved PID is active.

5. Send SIGHUP to the running process
   If the process exists, sends the SIGHUP signal using kill -SIGHUP to prompt the container to reload.

6. Logging with timestamps
   Each outcome (success or failure) logs a message with the current ISO-8601 timestamp using date -Is.

Important Implementation Details

• The script runs with set -eu which ensures it exits on any unset variables (-u) or errors (-e), improving robustness.

• It requires sudo privileges for Docker commands and to send signals to processes, implying it should be run by a user with appropriate permissions.

• The search for the container is based on Docker Compose service labeling, making it specific to environments using Docker Compose with this label convention.

• The use of ps -e | grep -q -e $pid checks for process existence but might incorrectly match substrings; however, this is unlikely for numeric PIDs and is a common lightweight check.

Detailed Command Descriptions

Usage Example

./bm-rotate.sh

The script can be executed manually or integrated into automation workflows where sending a SIGHUP to the block manager container is required, for example, after configuration changes.

Interaction with Other System Components

• Docker Engine: Utilizes Docker CLI commands (docker ps, docker inspect) to interact with container metadata and state.

• Block Manager Service: Targets the container running the block_manager service (identified by Docker Compose label).

• Host OS Process Management: Uses process signals (kill -SIGHUP) and process listing (ps) to control container processes at the OS level.

This script is intended to be part of operational scripts managing container lifecycle or signaling for configuration reloads without container restarts.

Mermaid Flowchart Diagram

flowchart TD
A[Start] --> B{Find container ID}
B -->|Found| C[Get container PID]
B -->|Not Found| G[Log "Couldn't find Block Manager container"]
C --> D{Is PID process running?}
D -->|Yes| E[Send SIGHUP to PID]
D -->|No| F[Log "Couldn't find Block Manager container process"]
E --> H[Log "SIGHUP sent"]
F --> I[End]
G --> I
H --> I

This flowchart illustrates the decision points and main actions within the script, highlighting the conditional checks on container and process existence followed by signaling and logging steps.