Audit devices are the components in Vault that keep a detailed log of all requests and response to Vault. Because every operation with Vault is an API request/response, the audit log contains every authenticated interaction with Vault, including errors.
Multiple audit devices can be enabled and Vault will send the audit logs to both. This allows you to not only have a redundant copy, but also a second copy in case the first is tampered with.
Each line in the audit log is a JSON object. The
type field specifies what
type of object it is. Currently, only two types exist:
The line contains all of the information for any given request and response. By
default, all the sensitive information is first hashed before logging in the
The audit logs contain the full request and response objects for every interaction with Vault. The request and response can be matched utilizing a unique identifier assigned to each request.
With a few specific exceptions, all strings (including authentication tokens and lease information) contained within requests and
responses are hashed with a salt using HMAC-SHA256. The purpose of the hash is
so that secrets aren't in plaintext within your audit logs. However, you're
still able to check the value of secrets by generating HMACs yourself; this can
be done with the audit device's hash function and salt by using the
/sys/audit-hash API endpoint (see the documentation for more details).
Note that currently only strings coming from JSON or being returned in JSON are HMAC'd. Other data types, like integers, booleans, and so on, are passed through in plaintext.
Enabling/Disabling Audit Devices
When a Vault server is first initialized, no auditing is enabled. Audit
devices must be enabled by a root user using
vault audit enable.
When enabling an audit device, options can be passed to it to configure it. For example, the command below enables the file audit device:
$ vault audit enable file file_path=/var/log/vault_audit.log
In the command above, we passed the "file_path" parameter to specify the path where the audit log will be written to. Each audit device has its own set of parameters. See the documentation to the left for more details.
When an audit device is disabled, it will stop receiving logs immediately. The existing logs that it did store are untouched.
Blocked Audit Devices
If there are any audit devices enabled, Vault requires that at least one be able to persist the log before completing a Vault request.
If you have only one audit device enabled, and it is blocking (network block, etc.), then Vault will be unresponsive. Vault will not complete any requests until the audit device can write.
If you have more than one audit device, then Vault will complete the request as long as one audit device persists the log.
Vault will not respond to requests if audit devices are blocked because audit logs are critically important and ignoring blocked requests opens an avenue for attack. Be absolutely certain that your audit devices cannot block.
Audit devices also have a full HTTP API. Please see the Audit device API docs for more details.