How to store and query logs
You should store logs to detect any potential errors within infrastructure and to respond to security incidents.
Use Splunk to store and query infrastructure, application and audit logs.
Splunk is a cloud-based SaaS tool for short and long-term storage, visualisation, alerting, and reporting.
Your product should have a proportionate design for short and long term storage of logs and ensuring the Confidentiality, Integrity, and Availability of logs.
The NCSC Cyber Assessment Framework, which GDS must comply with, has an entire category dedicated to Security Monitoring.
Logit deprecation notice
The shared GDS Logit account can still be used for existing environments; however, you should use Splunk for new logging requirements.
Logit offers cloud-based on-demand, shared ELK (Elasticsearch, Logstash and Kibana) stacks as a service. They are suitable for short-term storage of logs, and are accessible and queryable.
Short-term storage
You should not need to store logs spanning long periods in your short-term queryable store. Practical retention periods for short-term queryable logs are:
- no more than 7 days for non-production environments
- no more than 30 days production environments
You should consider storing security and audit events for up to a year, this is because the average MTTD (Mean Time to Detect) is 204 days (over 6 months) to identify a breach, according to a 2023 IBM data breach study.
Your product may have legal or other requirements determining how long you should store logs. For example, the Payment Card Industry Data Security Standard (PCI-DSS) requires 3 months of easily accessible logs and 12 months of archived logs.
Long-term storage
When storing logs, you should focus on long-term durability for compliance reasons or to identify long-term performance trends.
Splunk is appropriate for up to a year of storage. If you require more, Splunk can be configured to archive data to your own S3 bucket - this saves files in a proprietary format so consider archiving to S3 in human-readable files using your own process.
Log shipping
If you have set up log shipping, you should consider:
- how your logs will get to short and long-term stores - we recommend using Amazon CloudWatch to collect logs and subscribing to the Cyber Security team’s Centralised Security Logging Service (CSLS).
- what happens if one of these stores is unavailable
- whether the store will be overloaded when it comes back online
You could have one process to ship logs to your long-term archive, and a second process to fill a short-term query tool from the long-term archive, for example you could combine Splunk with Amazon Cloudwatch and also archive to S3.
CSLS utilises Amazon Kinesis and can persist logs in the event that Splunk is unavailable and will resume sending data when Splunk is available again.
Splunk Cloud’s recommended input is the HTTP Event Collector (HEC) - CSLS uses this.
Note: Splunk Cloud does not support syslog, you may need a forwarder if syslog is your only output option:
Filtering out sensitive information
You should ensure that sensitive information, such as query parameters containing personally identifiable information (PII), is filtered out before logs are shipped. Make use of log filtering mechanisms which may be present in the application framework you are using, such as in Ruby on Rails.
Structured logging
In order to allow for rich querying of log data you should ensure that your logs are in a structured format.
Stuctured logging with Splunk
Splunk automatically parses JSON log lines. Other formats may need specific field extracts configured in Splunk.
For interoperability with pre-built apps and alerting, it is beneficial to align your logs to the Splunk CIM (Common Information Model).
The Web CIM is most commonly used at GDS - it specifies particular field
names for data, for example:
http_user_agentfor the client’s user agentsrcfor the source IP addressdestfor the origin server IP address
Access to Splunk
Access control for GDS users is managed by the IT Service Desk, use the
helpdesk to request access. If you’re unsure what role you should be
requesting, ask in the #cyber-security-help Slack channel.
Advice for particular frameworks or platforms
Dropwizard
The dropwizard-logstash library will set things up for you using the standard names. Splunk will be able to ingest this format.
GOV.UK PaaS (Cloud Foundry)
There is broker documentation describing how drain logs to Splunk via Centralised Security Logging Service (CSLS).
The GOV.UK PaaS Logging documentation will help you configure Logit and drain logs into it from your app.