Common Issues with Index Migration

Oct 13, 2025 by thesweetdesigns.com 34 views

Background

Opensearch is a powerful search and analytics engine that provides a scalable and flexible solution for indexing and querying large datasets. However, like any complex system, Opensearch is not immune to issues and errors that can occur during the migration of indices through their life cycle. In this article, we will explore the common issues that can cause index migration failures in Opensearch and provide a programmatic solution to handle these failures.

Common Issues with Index Migration

Indices in Opensearch can get stuck during their migration through the life cycle at two critical points:

Transitioning from Hot to Warm

When an index is transitioning from hot to warm, it can get stuck due to two main reasons:

1. Insufficient Warm Node Count

If the warm node count is insufficient, the index may not be able to transition to warm, resulting in a failure. In this case, the solution is to increase the warm node count if necessary.

2. Large Shards

If the shards of the index are too large, it can cause the index to get stuck during the transition to warm. In this case, the solution is to reindex the large index and move it to warm manually. If this is a common issue, it may be necessary to increase the number of shards for that index.

Transitioning from Warm to Cold

When an index is transitioning from warm to cold, it can get stuck due to two main reasons:

1. Index Already Exists in Cold

If an index already exists in cold, it can cause the index to get stuck during the transition. In this case, there are two possible solutions:

1. Delete Residue in Warm

If the index is largely moved over, the solution is to delete the residue in warm. This is usually a small amount of data, with only a handful of documents. However, it is essential to ensure that the leftover index in warm is a fraction (< 1%) of the cold size before deleting it.

2. Delete Smaller Cold Index and Retry

If the index needs to be started again, the solution is to delete the smaller cold index and retry the transition process.

Programmatic Solution to Handle Index Migration Failures

To provide insight into the indices that are problematic, it would be great to create a new report in Hoodaw and keep an eye on failed indices. Not all indices will be programmatically handled, but a programmatic solution can help to automate the process and reduce the manual effort required.

To trigger an alert, it would be useful to add a CloudWatch alarm. This can help to notify the team when an index migration failure occurs, allowing them to take prompt action to resolve the issue.

Code Example: Opensearch Index Migration Failure Handler

Here is an example of a programmatic solution to handle index migration failures in Opensearch:

import boto3
from opensearchpy import OpenSearch

# Initialize Opensearch client
es = OpenSearch(hosts=['https://your-opensearch-domain.com:9200'])

# Define a function to handle index migration failures
def handle_index_migration_failure(index_name):
    # Check if the index exists in warm
    warm_indices = es.indices.get(index=index_name)
    if warm_indices['index']['warm']:
        # Check if the index already exists in cold
        cold_indices = es.indices.get(index=index_name)
        if cold_indices['index']['cold']:
            # Delete residue in warm
            es.indices.delete(index=index_name, ignore=[404])
        else:
            # Delete smaller cold index and retry
            es.indices.delete(index=index_name, ignore=[404])
            es.indices.create(index=index_name, body={'settings': {'index': {'warm': True}}})
    else:
        # Increase warm node count if necessary
        es.indices.put_settings(index=index_name, body={'settings': {'index': {'warm': True}}})

# Define a function to trigger an alert
def trigger_alert(index_name):
    # Create a CloudWatch alarm
    cloudwatch = boto3.client('cloudwatch')
    cloudwatch.put_metric_alarm(
        AlarmName=index_name + '-index-migration-failure',
        ComparisonOperator='GreaterThanThreshold',
        EvaluationPeriods=1,
        MetricName='IndexMigrationFailure',
        Namespace='Opensearch',
        Period=300,
        Statistic='Sum',
        Threshold=1,
        ActionsEnabled=True,
        AlarmActions=['arn:aws:sns:your-region:your-account-id:your-sns-topic']
    )

# Define a function to monitor index migration failures
def monitor_index_migration_failures():
    # Get a list of indices that are transitioning from hot to warm
    hot_to_warm_indices = es.indices.get(index='*')
    for index in hot_to_warm_indices['indices']:
        if index['warm']:
            # Handle index migration failure
            handle_index_migration_failure(index['name'])
            # Trigger an alert
            trigger_alert(index['name'])

# Run the monitor function every 5 minutes
import schedule
import time
schedule.every(5).minutes.do(monitor_index_migration_failures)

while True:
    schedule.run_pending()
    time.sleep(1)

This code example demonstrates a programmatic solution to handle index migration failures in Opensearch. It defines three functions:

handle_index_migration_failure: This function handles index migration failures by checking if the index exists in warm and cold, and deleting the residue in warm or deleting the smaller cold index and retrying the transition process.
trigger_alert: This function triggers an alert by creating a CloudWatch alarm.
monitor_index_migration_failures: This function monitors index migration failures by getting a list of indices that are transitioning from hot to warm, handling index migration failures, and triggering an alert.

The code uses the schedule library to run the monitor_index_migration_failures function every 5 minutes.

Conclusion

Q: What are the common issues that can cause index migration failures in Opensearch?

A: The common issues that can cause index migration failures in Opensearch are:

Insufficient warm node count
Large shards
Index already exists in cold
Residue in warm

Q: How can I increase the warm node count if necessary?

A: To increase the warm node count if necessary, you can use the put_settings API in Opensearch. Here is an example of how to do it:

es.indices.put_settings(index=index_name, body={'settings': {'index': {'warm': True}}})

Q: How can I reindex a large index and move it to warm manually?

A: To reindex a large index and move it to warm manually, you can use the reindex API in Opensearch. Here is an example of how to do it:

es.reindex(
    body={
        'source': {
            'index': index_name
        },
        'dest': {
            'index': index_name + '_warm'
        }
    }
)

Q: How can I delete residue in warm?

A: To delete residue in warm, you can use the delete API in Opensearch. Here is an example of how to do it:

es.indices.delete(index=index_name, ignore=[404])

Q: How can I delete a smaller cold index and retry the transition process?

A: To delete a smaller cold index and retry the transition process, you can use the delete API in Opensearch. Here is an example of how to do it:

es.indices.delete(index=index_name, ignore=[404])
es.indices.create(index=index_name, body={'settings': {'index': {'warm': True}}})

Q: How can I trigger an alert when an index migration failure occurs?

A: To trigger an alert when an index migration failure occurs, you can use the put_metric_alarm API in CloudWatch. Here is an example of how to do it:

cloudwatch.put_metric_alarm(
    AlarmName=index_name + '-index-migration-failure',
    ComparisonOperator='GreaterThanThreshold',
    EvaluationPeriods=1,
    MetricName='IndexMigrationFailure',
    Namespace='Opensearch',
    Period=300,
    Statistic='Sum',
    Threshold=1,
    ActionsEnabled=True,
    AlarmActions=['arn:aws:sns:your-region:your-account-id:your-sns-topic']
)

Q: How can I monitor index migration failures in Opensearch?

A: To monitor index migration failures in Opensearch, you can use the get API to get a list of indices that are transitioning from hot to warm, and then handle each index migration failure individually. Here is an example of how to do it:

hot_to_warm_indices = es.indices.get(index='*')
for index in hot_to_warm_indices['indices']:
    if index['warm']:
        handle_index_migration_failure(index['name'])

Q: What is the best way to handle index migration failures in Opensearch?

A: The best way to handle index migration failures in Opensearch is to create a programmatic solution that can automate the process of handling index migration failures. This can be done by using the schedule library to run a function every 5 minutes that checks for index migration failures and handles them accordingly.

Q: Can I use this code example as a starting point for implementing a similar solution in my own environment?

A: Yes, you can use this code example as a starting point for implementing a similar solution in your own environment. However, you will need to modify the code to fit your specific use case and requirements.

Q: What are some best practices for handling index migration failures in Opensearch?

A: Some best practices for handling index migration failures in Opensearch include:

Creating a programmatic solution to automate the process of handling index migration failures
Using the schedule library to run a function every 5 minutes that checks for index migration failures and handles them accordingly
Using the put_metric_alarm API in CloudWatch to trigger an alert when an index migration failure occurs
Monitoring index migration failures in Opensearch using the get API to get a list of indices that are transitioning from hot to warm, and then handling each index migration failure individually.