# GitLab Developers Guide to Logging [GitLab Logs](../administration/logs.md) play a critical role for both administrators and GitLab team members to diagnose problems in the field. ## Don't use `Rails.logger` Currently `Rails.logger` calls all get saved into `production.log`, which contains a mix of Rails' logs and other calls developers have inserted in the code base. For example: ``` Started GET "/gitlabhq/yaml_db/tree/master" for 168.111.56.1 at 2015-02-12 19:34:53 +0200 Processing by Projects::TreeController#show as HTML Parameters: {"project_id"=>"gitlabhq/yaml_db", "id"=>"master"} ... Namespaces"."created_at" DESC, "namespaces"."id" DESC LIMIT 1 [["id", 26]] CACHE (0.0ms) SELECT "members".* FROM "members" WHERE "members"."source_type" = 'Project' AND "members"."type" IN ('ProjectMember') AND "members"."source_id" = $1 AND "members"."source_type" = $2 AND "members"."user_id" = 1 ORDER BY "members"."created_at" DESC, "members"."id" DESC LIMIT 1 [["source_id", 18], ["source_type", "Project"]] CACHE (0.0ms) SELECT "members".* FROM "members" WHERE "members"."source_type" = 'Project' AND "members". (1.4ms) SELECT COUNT(*) FROM "merge_requests" WHERE "merge_requests"."target_project_id" = $1 AND ("merge_requests"."state" IN ('opened','reopened')) [["target_project_id", 18]] Rendered layouts/nav/_project.html.haml (28.0ms) Rendered layouts/_collapse_button.html.haml (0.2ms) Rendered layouts/_flash.html.haml (0.1ms) Rendered layouts/_page.html.haml (32.9ms) Completed 200 OK in 166ms (Views: 117.4ms | ActiveRecord: 27.2ms) ``` These logs suffer from a number of problems: 1. They often lack timestamps or other contextual information (e.g. project ID, user) 1. They may span multiple lines, which make them hard to find via Elasticsearch. 1. They lack a common structure, which make them hard to parse by log forwarders, such as Logstash or Fluentd. This also makes them hard to search. Note that currently on GitLab.com, any messages in `production.log` will NOT get indexed by Elasticsearch due to the sheer volume and noise. They do end up in Google Stackdriver, but it is still harder to search for logs there. See the [GitLab.com logging documentation](https://gitlab.com/gitlab-com/runbooks/blob/master/howto/logging.md) for more details. ## Use structured (JSON) logging Structured logging solves these problems. Consider the example from an API request: ```json {"time":"2018-10-29T12:49:42.123Z","severity":"INFO","duration":709.08,"db":14.59,"view":694.49,"status":200,"method":"GET","path":"/api/v4/projects","params":[{"key":"action","value":"git-upload-pack"},{"key":"changes","value":"_any"},{"key":"key_id","value":"secret"},{"key":"secret_token","value":"[FILTERED]"}],"host":"localhost","ip":"::1","ua":"Ruby","route":"/api/:version/projects","user_id":1,"username":"root","queue_duration":100.31,"gitaly_calls":30} ``` In a single line, we've included all the information that a user needs to understand what happened: the timestamp, HTTP method and path, user ID, etc. ### How to use JSON logging Suppose you want to log the events that happen in a project importer. You want to log issues created, merge requests, etc. as the importer progresses. Here's what to do: 1. Look at [the list of GitLab Logs](../administration/logs.md) to see if your log message might belong with one of the existing log files. 1. If there isn't a good place, consider creating a new filename, but check with a maintainer if it makes sense to do so. A log file should make it easy for people to search pertinent logs in one place. For example, `geo.log` contains all logs pertaining to GitLab Geo. To create a new file: 1. Choose a filename (e.g. `importer_json.log`). 1. Create a new subclass of `Gitlab::JsonLogger`: ```ruby module Gitlab module Import class Logger < ::Gitlab::JsonLogger def self.file_name_noext 'importer' end end end end ``` 1. In your class where you want to log, you might initialize the logger as an instance variable: ```ruby attr_accessor :logger def initialize @logger = Gitlab::Import::Logger.build end ``` Note that it's useful to memoize this because creating a new logger each time you log will open a file, adding unnecessary overhead. 1. Now insert log messages into your code. When adding logs, make sure to include all the context as key-value pairs: ```ruby # BAD logger.info("Unable to create project #{project.id}") ``` ```ruby # GOOD logger.info(message: "Unable to create project", project_id: project.id) ``` 1. Be sure to create a common base structure of your log messages. For example, all messages might have `current_user_id` and `project_id` to make it easier to search for activities by user for a given time. 1. Do NOT mix and match types. Elasticsearch won't be able to index your logs properly if you [mix integer and string types](https://www.elastic.co/guide/en/elasticsearch/guide/current/mapping.html#_avoiding_type_gotchas): ```ruby # BAD logger.info(message: "Import error", error: 1) logger.info(message: "Import error", error: "I/O failure") ``` ```ruby # GOOD logger.info(message: "Import error", error_code: 1, error: "I/O failure") ``` ## Additional steps with new log files 1. Consider log retention settings. By default, Omnibus will rotate any logs in `/var/log/gitlab/gitlab-rails/*.log` every hour and [keep at most 30 compressed files](https://docs.gitlab.com/omnibus/settings/logs.html#logrotate). On GitLab.com, that setting is only 6 compressed files. These settings should suffice for most users, but you may need to tweak them in [Omnibus GitLab](https://gitlab.com/gitlab-org/omnibus-gitlab). 1. If you add a new file, submit an issue to the [production tracker](https://gitlab.com/gitlab-com/gl-infra/production/issues) or a merge request to the [gitlab_fluentd](https://gitlab.com/gitlab-cookbooks/gitlab_fluentd) project. See [this example](https://gitlab.com/gitlab-cookbooks/gitlab_fluentd/merge_requests/51/diffs). 1. Be sure to update the [GitLab CE/EE documentation](../administration/logs.md) and the [GitLab.com runbooks](https://gitlab.com/gitlab-com/runbooks/blob/master/howto/logging.md).