Troubleshoot Compute

updated: 2019-08-23 18:48
Contents

Troubleshoot Compute

Common problems for Compute typically involve misconfigured networking or credentials that are not sourced properly in the environment. Also, most flat networking configurations do not enable ping or ssh from a compute node to the instances that run on that node. Another common problem is trying to run 32-bit images on a 64-bit compute node. This section shows you how to troubleshoot Compute.

Compute service logging

Compute stores a log file for each service in /var/log/nova. For example, nova-compute.log is the log for the nova-compute service. You can set the following options to format log strings for the nova.log module in the nova.conf file:

  • logging_context_format_string
  • logging_default_format_string

If the log level is set to debug, you can also specify logging_debug_format_suffix to append extra formatting. For information about what variables are available for the formatter, see Formatter Objects.

You have two logging options for OpenStack Compute based on configuration settings. In nova.conf, include the logfile option to enable logging. Alternatively you can set use_syslog = 1 so that the nova daemon logs to syslog.

Guru Meditation reports

A Guru Meditation report is sent by the Compute service upon receipt of the SIGUSR2 signal (SIGUSR1 before Mitaka). This report is a general-purpose error report that includes details about the current state of the service. The error report is sent to stderr.

For example, if you redirect error output to nova-api-err.log using nova-api 2>/var/log/nova/nova-api-err.log, resulting in the process ID 8675, you can then run:

# kill -USR2 8675

This command triggers the Guru Meditation report to be printed to /var/log/nova/nova-api-err.log.

The report has the following sections:

  • Package: Displays information about the package to which the process belongs, including version information.
  • Threads: Displays stack traces and thread IDs for each of the threads within the process.
  • Green Threads: Displays stack traces for each of the green threads within the process (green threads do not have thread IDs).
  • Configuration: Lists all configuration options currently accessible through the CONF object for the current process.

For more information, see Guru Meditation Reports.

Common errors and fixes for Compute

The ask.openstack.org site offers a place to ask and answer questions, and you can also mark questions as frequently asked questions. This section describes some errors people have posted previously. Bugs are constantly being fixed, so online resources are a great way to get the most up-to-date errors and fixes.

Credential errors, 401, and 403 forbidden errors

Problem

Missing credentials cause a 403 forbidden error.

Solution

To resolve this issue, use one of these methods:

  1. Manual method
    Gets the novarc file from the project ZIP file, saves existing credentials in case of override, and manually sources the novarc file.
  2. Script method
    Generates novarc from the project ZIP file and sources it for you.

When you run nova-api the first time, it generates the certificate authority information, including openssl.cnf. If you start the CA services before this, you might not be able to create your ZIP file. Restart the services. When your CA information is available, create your ZIP file.

Also, check your HTTP proxy settings to see whether they cause problems with novarc creation.

Instance errors

Problem

Sometimes a particular instance shows pending or you cannot SSH to it. Sometimes the image itself is the problem. For example, when you use flat manager networking, you do not have a DHCP server and certain images do not support interface injection; you cannot connect to them.

Solution

To fix instance errors use an image that does support this method, such as Ubuntu, which obtains an IP address correctly with FlatManager network settings.

To troubleshoot other possible problems with an instance, such as an instance that stays in a spawning state, check the directory for the particular instance under /var/lib/nova/instances on the nova-compute host and make sure that these files are present:

  • libvirt.xml
  • disk
  • disk-raw
  • kernel
  • ramdisk
  • console.log, after the instance starts.

If any files are missing, empty, or very small, the nova-compute service did not successfully download the images from the Image service.

Also check nova-compute.log for exceptions. Sometimes they do not appear in the console output.

Next, check the log file for the instance in the /var/log/libvirt/qemu directory to see if it exists and has any useful error messages in it.

Finally, from the /var/lib/nova/instances directory for the instance, see if this command returns an error:

# virsh create libvirt.xml

Empty log output for Linux instances

Problem

You can view the log output of running instances from either the Log tab of the dashboard or the output of nova console-log. In some cases, the log output of a running Linux instance will be empty or only display a single character (for example, the ? character).

This occurs when the Compute service attempts to retrieve the log output of the instance via a serial console while the instance itself is not configured to send output to the console.

Solution

To rectify this, append the following parameters to kernel arguments specified in the instance’s boot loader:

console=tty0 console=ttyS0,115200n8

Upon rebooting, the instance will be configured to send output to the Compute service.

Reset the state of an instance

Problem

Instances can remain in an intermediate state, such as deleting.

Solution

You can use the nova reset-state command to manually reset the state of an instance to an error state. You can then delete the instance. For example:

$ nova reset-state c6bbbf26-b40a-47e7-8d5c-eb17bf65c485
$ openstack server delete c6bbbf26-b40a-47e7-8d5c-eb17bf65c485

You can also use the --active parameter to force the instance back to an active state instead of an error state. For example:

$ nova reset-state --active c6bbbf26-b40a-47e7-8d5c-eb17bf65c485

Injection problems

Problem

Instances may boot slowly, or do not boot. File injection can cause this problem.

Solution

To disable injection in libvirt, set the following in nova.conf:

[libvirt]
inject_partition = -2

Note

If you have not enabled the configuration drive and you want to make user-specified files available from the metadata server for to improve performance and avoid boot failure if injection fails, you must disable injection.

Disable live snapshotting

Problem

Administrators using libvirt version 1.2.2 may experience problems with live snapshot creation. Occasionally, libvirt version 1.2.2 fails to create live snapshots under the load of creating concurrent snapshot.

Solution

To effectively disable the libvirt live snapshotting, until the problem is resolved, configure the disable_libvirt_livesnapshot option. You can turn off the live snapshotting mechanism by setting up its value to True in the [workarounds] section of the nova.conf file:

[workarounds]
disable_libvirt_livesnapshot = True
updated: 2019-08-23 18:48
Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.

found an error? report a bug questions?