policy-bot
is a GitHub App for enforcing
approval policies on pull requests. It does this by creating a status check,
which can be configured as a required status check.
While GitHub natively supports required reviews, policy-bot
provides more
complex approval features:
- Require reviews from specific users, organizations, or teams
- Apply rules based on the files, authors, or branches involved in a pull request
- Combine multiple approval rules with
and
andor
conditions - Automatically approve pull requests that meet specific conditions
Behavior is configured by a file in each repository. policy-bot
also provides a
UI to view the detailed approval status of any pull request.
- Configuration
- Security
- Deployment
- Development
- Contributing
- License
Policies are defined by a .policy.yml
file at the root of the repository.
You can change this path and file name when running your own instance of the
server.
-
The file is read from the most recent commit on the target branch of each pull request.
-
The file may contain a reference to a policy in a different repository (see Remote Policy Configuration.)
-
If the file does not exist in the repository,
policy-bot
tries to load a sharedpolicy.yml
file at the root of the.github
repository in the same organization. You can change this path and repository name when running your own instance of the server. -
If a policy does not exist in the repository or in the shared organization repository,
policy-bot
does not post a status check on the pull request. This means it is safe to enablepolicy-bot
on all repositories in an organization.
The overall policy is expressed by:
- Lists of rule definitions
- A set of policies that combine the rules or define additional options
Consider the following example, which allows changes to certain paths without
review, but all other changes require review from the palantir/devtools
.
Any member of the palantir
organization can also disapprove changes.
# the high level policy
policy:
approval:
- or:
- the devtools team has approved
- only staging files have changed
disapproval:
requires:
organizations:
- "palantir"
# the list of rules
approval_rules:
- name: the devtools team has approved
requires:
count: 1
teams:
- "palantir/devtools"
- name: only staging files have changed
if:
only_changed_files:
paths:
- "staging/.*"
requires:
count: 0
The YAML language specification supports flow scalars (basic values like strings
and numbers) in three formats:
single-quoted,
double-quoted, and
plain. Each support different
escape characters, which can cause confusion when used for regex strings
(which often contain the \\
character).
- Single Quoted:
'
is used as an escape character. Backslash characters do not need to be escaped. e.g.'^BREAKING CHANGE: (\w| )+$'
- Double Quoted:
\
is used as an escape character. Backslash characters must be escaped with a preceding\
. e.g."^BREAKING CHANGE: (\\w| )+$"
- Plain: There are no escape characters. Backslash characters do not need to be escaped.
e.g.
^BREAKING CHANGE: (\w| )+$
You can also define a remote policy by specifying a repository, path, and ref
(only repository is required). Instead of defining a policy
key, you would
define a remote
key. Only 1 level of remote configuration is supported by design.
# The remote repository to read the policy file from. This is required, and must
# be in the form of "org/repo-name". The policy bot github app must have read
# access to this repository.
remote: org/repo-name
# The path to the policy config file in the remote repository. If none is
# specified, the default path in the server config is used.
path: path/to/policy.yml
# The branch (or tag, or commit hash) that should be used on the remote
# repository. If none is specified, the default branch of the repository is used.
ref: master
Each list entry in approval_rules
has the following specification:
# "name" is required, and is used to reference rules in the "policy" block
name: "example rule"
# "description" is optional and provides an explanation of the rule or
# additional help for users. Unlike YAML comments, it appears in the pull
# request details UI along with other information about the rule.
description: "A rule that explains how to configure all of the features"
# "if" specifies a set of predicates that must be true for the rule to apply.
# This block, and every condition within it are optional. If the block does not
# exist, the rule applies to every pull request.
if:
# "changed_files" is satisfied if any file in the pull request matches any
# regular expression in the "paths" list. If the "ignore" list is present,
# files in the pull request matching these regular expressions are ignored
# by this rule.
#
# Note: Double-quote strings must escape backslashes while single/plain do not.
# See the Notes on YAML Syntax section of this README for more information.
changed_files:
paths:
- "config/.*"
- "server/views/.*\\.tmpl"
ignore:
- "config/special\\.file"
# "only_changed_files" is satisfied if all files changed by the pull request
# match at least one regular expression in the list.
#
# Note: Double-quote strings must escape backslashes while single/plain do not.
# See the Notes on YAML Syntax section of this README for more information.
only_changed_files:
paths:
- "config/.*"
# "has_author_in" is satisfied if the user who opened the pull request is in
# the users list or belongs to any of the listed organizations or teams. The
# `users` field can contain a GitHub App by appending `[bot]` to the end of
# the name, for example: `fun-github-app[bot]`
has_author_in:
users: ["user1", "user2", ...]
organizations: ["org1", "org2", ...]
teams: ["org1/team1", "org2/team2", ...]
# "has_contributor_in" is satisfied if any commits on the pull request have
# an author or committer in the users list or that belong to any of the
# listed organizations or teams.
has_contributor_in:
users: ["user1", "user2", ...]
organizations: ["org1", "org2", ...]
teams: ["org1/team1", "org2/team2", ...]
# "only_has_contributors_in" is satisfied if all of the commits on the pull
# request have an author or committer in the users list or that belong to
# any of the listed organizations or teams.
only_has_contributors_in:
users: ["user1", "user2", ...]
organizations: ["org1", "org2", ...]
teams: ["org1/team1", "org2/team2", ...]
# "author_is_only_contributor", when true, is satisfied if all commits in the
# pull request are authored by and committed by the user who opened the pull
# request. When false, it is satisfied if at least one commit in the pull
# request was authored or committed by another user.
author_is_only_contributor: true
# "targets_branch" is satisfied if the target branch of the pull request
# matches the regular expression
#
# Note: Double-quote strings must escape backslashes while single/plain do not.
# See the Notes on YAML Syntax section of this README for more information.
targets_branch:
pattern: "^(master|regexPattern)$"
# "from_branch" is satisfied if the source branch of the pull request
# matches the regular expression. Note that source branches from forks will
# have the pattern "repo_owner:branch_name"
#
# Note: Double-quote strings must escape backslashes while single/plain do not.
# See the Notes on YAML Syntax section of this README for more information.
from_branch:
pattern: "^(master|regexPattern)$"
# "modified_lines" is satisfied if the number of lines added or deleted by
# the pull request matches any of the listed conditions. Each expression is
# an operator (one of '<' or '>'), an optional space, and a number.
modified_lines:
additions: "> 100"
deletions: "> 100"
total: "> 200"
# "has_successful_status" is satisfied if the status checks that are specified
# are marked successful on the head commit of the pull request.
has_successful_status:
- "status-name-1"
- "status-name-2"
- "status-name-3"
# "has_labels" is satisfied if the pull request has the specified labels
# applied
has_labels:
- "label-1"
- "label-2"
# "title" is satisfied if the pull request title matches any one of the
# patterns within the "matches" list, and does not match all of the patterns
# within the "not_matches" list.
# e.g. this predicate triggers for titles including "BREAKING CHANGE" or titles
# that are not marked as docs/style/chore changes (using conventional commits
# formatting)
#
# Note: Double-quote strings must escape backslashes while single/plain do not.
# See the Notes on YAML Syntax section of this README for more information.
title:
matches:
- "^BREAKING CHANGE: (\\w| )+$"
not_matches:
- "^(docs|style|chore): (\\w| )+$"
# "has_valid_signatures" is satisfied if the commits in the pull request
# all have git commit signatures that have been verified by GitHub
has_valid_signatures: true
# "has_valid_signatures_by" is satisfied if the commits in the pull request
# all have git commit signatures that have been verified by GitHub, and
# the authenticated signatures are attributed to a user in the users list
# or belong to a user in any of the listed organizations or teams.
has_valid_signatures_by:
users: ["user1", "user2", ...]
organizations: ["org1", "org2", ...]
teams: ["org1/team1", "org2/team2", ...]
# "has_valid_signatures_by_keys" is satisfied if the commits in the pull request
# all have git commit signatures that have been verified by GitHub, and
# the authenticated signatures are attributed to a GPG key with an ID in the list.
has_valid_signatures_by_keys:
key_ids: ["3AA5C34371567BD2"]
# "options" specifies a set of restrictions on approvals. If the block does not
# exist, the default values are used.
options:
# If true, approvals by the author of a pull request are considered when
# calculating the status. False by default.
allow_author: false
# If true, the approvals of someone who has committed to the pull request are
# considered when calculating the status. The pull request author is considered
# a contributor. If allow_author and allow_contributor would disagree, this option
# always wins. False by default.
allow_contributor: false
# If true, pushing new commits to a pull request will invalidate existing
# approvals for this rule. False by default.
invalidate_on_push: false
# If true, comments on PRs and review comments that have been edited in any way
# will be ignored when evaluating approval rules. Default is false.
ignore_edited_comments: false
# If true, "update merges" do not invalidate approval (if invalidate_on_push
# is enabled) and their authors/committers do not count as contributors. An
# "update merge" is a merge commit that was created in the UI or via the API
# and merges the target branch into the pull request branch. These are
# commonly created by using the "Update branch" button in the UI.
ignore_update_merges: false
# If present, commits authored and committed by users meeting the conditions
# are ignored for the purposes of approval. This means the users will not
# count as contributors and their commits will not invalidate approval if
# invalidate_on_push is enabled. Both the author and the committer must match
# the conditions to ignore the commit. This option has security implications,
# see the README for more details.
ignore_commits_by:
users: ["bulldozer[bot]"]
organizations: ["org1"]
teams: ["org1/team1"]
# Automatically request reviewers when a Pull Request is opened
# if this rule is pending, there are no assigned reviewers, and if the
# Pull Request is not in Draft.
# Reviewers are selected based on the set of requirements for this rule
# and reviewers can be augmented using the mode option.
request_review:
# False by default
enabled: true
# mode modifies how reviewers are selected. `all-users` will request all users
# who are able to approve the pending rule. `random-users` selects a small
# set of random users based on the required count of approvals. `teams` will
# request teams to review. Teams must have explicit access defined under
# https://github.com/<org>/<repo>/settings/access in order to be tagged,
# at least until https://github.com/palantir/policy-bot/issues/165 is fixed.
# Defaults to 'random-users'.
mode: all-users|random-users|teams
# "methods" defines how users may express approval.
methods:
# If a comment contains a string in this list, it counts as approval. Use
# the "comment_patterns" option if you want to match full comments. The
# default values are shown.
comments:
- ":+1:"
- "π"
# If a comment matches a regular expression in this list, it counts as
# approval. Defaults to an empty list.
#
# Note: Double-quote strings must escape backslashes while single/plain do not.
# See the Notes on YAML Syntax section of this README for more information.
comment_patterns:
- "^Signed-off by \\s+$"
# If true, GitHub reviews can be used for approval. All GitHub review approvals
# will be accepted as approval candidates. Default is true.
github_review: true
# Just like the "comment_patterns" option, but for GitHub reviews. Only GitHub
# review approvals matching the included patterns will be accepted as
# approval candidates. Defaults to an empty list.
github_review_comment_patterns:
- '\b(?i)domain\s*lgtm\b'
# "requires" specifies the approval requirements for the rule. If the block
# does not exist, the rule is automatically approved.
requires:
# "count" is the number of required approvals. The default is 0, meaning no
# approval is necessary.
count: 1
# A user must be in the list of users or belong to at least one of the given
# organizations or teams for their approval to count for this rule.
users: ["user1", "user2"]
organizations: ["org1", "org2"]
teams: ["org1/team1", "org2/team2"]
# A user must have at least the minimum permission in this list for their
# approval to count for this rule. Valid permissions are "admin", "maintain",
# "write", "triage", and "read".
#
# Specifying more than one permission is only useful to control which users
# or teams are selected for review requests. See the documentation on review
# requests for details.
permissions: ["write"]
# Deprecated: use 'permissions: ["admin"]'
#
# Allows approval by admins of the org or repository
# admins: true
# Deprecated: use 'permissions: ["write"]'
#
# Allows approval by users who have write on the repository
# write_collaborators: true
The approval
block in the policy
section defines a list of rules that must
all be true:
policy:
approval:
- rule1
- rule2
- rule3
- ...
Each list entry may be the name of a rule, or one of the following conjunctions:
or:
- rule1
- rule2
- ...
and:
- rule1
- rule2
- ...
Conjunctions can contain more conjunctions (up to a maximum depth of 5):
- or:
- rule1
- rule2
- and:
- rule3
- rule4
Disapproval allows users to explicitly block pull requests if certain changes must be made. Any member of in the set of allowed users can disapprove a change or revoke another user's disapproval.
Unlike approval, all disapproval predicates and options are specified as part
of the policy. Effectively, there is a single disapproval rule. The disapproval
policy has the following specification:
# "disapproval" is the top-level key in the policy block.
disapproval:
# "if" specifies a set of predicates which will cause disapproval if any are
# true
#
# This block, and every condition within it are optional. If the block does
# not exist, a pull request is only disapproved if a user takes a disapproval
# action.
if:
# All predicates from the approval rules section are valid here
title:
not_matches:
- "^(fix|feat|chore): (\\w| )+$"
- "^BREAKING CHANGE: (\\w| )+$"
matches:
- "^BLOCKED"
# "options" sets behavior related to disapproval. If it does not exist, the
# defaults shown below are used.
options:
# "methods" defines how users set and revoke disapproval.
methods:
# "disapprove" sets the methods for disapproval.
disapprove:
comments:
- ":-1:"
- "π"
github_review: true
# "revoke" sets the methods for revoking disapproval. Usually, these will
# match the methods used by approval rules.
revoke:
comments:
- ":+1:"
- "π"
github_review: true
# "requires" sets the users that are allowed to disapprove. If it is not set,
# disapproval is not enabled.
requires:
users: ["user1", "user2"]
organizations: ["org1", "org2"]
teams: ["org1/team1", "org2/team2"]
Sometimes it is useful to test if a given policy file is valid, especially in a CI environment.
An API endpoint exists at /api/validate
to validate the syntax of the yaml and policy configuration,
however it cannot validate that the rules are semantically correct for a given use case.
The API can be used as such:
$ curl https://policybot.domain/api/validate -XPUT -T path/to/policy.yml
{"message":"failed to parse approval policy: failed to parse subpolicies for 'and': policy references undefined rule 'the devtools team has approved', allowed values: [the devtools team has]","version":"1.12.5"}
You can examine the HTTP response code to automatically detect failures
$ rcode=$(curl https://policybot.domain/api/validate -XPUT -T path/to/policy.yml -s -w "%{http_code}" -o /tmp/response)
$ if [[ "${rcode}" -gt 299 ]]; then cat /tmp/response && exit 1; fi
There are several additional behaviors that follow from the rules above that are worth mentioning.
You must set at least one of the disapproval.requires
fields to enable
disapproval. Without setting one of these fields, GitHub reviews that request
changes have no effect on the policy-bot
status.
GitHub Reviews allow a user to dismiss the last review they left, causing it
to no longer count towards rule evaluations. When this happens
policy-bot
will use a previous, non-dismissed review, if it exists, when evaluating
rules.
For example, if a user leaves an "approval" review and follows up with a
"request changes" review, policy-bot
will use the "request changes" review when
evaluating rules. However, if the user then dimisses their "request changes"
review, policy-bot
will instead use the initial "approval" review in evaluating
any rules
If the if
block of a rule (the predicate) is not satisfied, the rule is
marked as "skipped". Skipped rules interact with or
and and
as follows:
- An
and
block containing only skipped rules is also skipped - An
or
block containing only skipped rules is also skipped
Effectively, skipped rules are treated as if they don't exist.
policy-bot
allows approval rules to reference organizations and teams that are
not in the organization that owns the repository where the rules appear. In
this case, policy-bot
must be installed on all referenced organizations.
For a commit on a branch to count as an "update merge" for the purpose of the
ignore_update_merges
option, the following must be true:
- The commit must have exactly two parents
- The commit must have the
committedViaWeb
property set totrue
- The first parent must exist in the pull request while the second parent must not exist in the pull request (meaning it is on the target branch)
These will all be true after updating a branch using the UI, but historic merges on long-running branches or merges created with the API may not be ignored. If this happens, you will need to reapprove the pull request.
This feature has security implications.
policy-bot
can automatically request reviewers for all pending rules
when Pull Requests are opened by setting the request_review
option.
The mode
enum modifies how reviewers are selected. There are currently three
supported options:
all-users
to request all users who can approverandom-users
to randomly select the number of users that are requiredteams
to request teams for review. Teams must be repository collaborators with at least read access.
options:
request_review:
enabled: true
mode: all-users|random-users|teams
The set of requested reviewers will not include the author of the pull request or users who are not collaborators on the repository.
When requesting reviews for rules that use repository permissions to select
approvers, only users who are direct collaborators or members of
repository teams are eligible for review selection. The users or their teams
must be granted an exact permission specified in the permissions
list of the
rule.
For example, if a rule can be approved by any user with admin
permission,
only direct or team admins are selected for review. Users who inherit
repository admin
permissions as organization owners are not selected.
The teams
mode needs the team visibility to be set to visibile
to enable this functionality for a given team.
Given the following example requirement rule,
requires:
count: 2
users: ["user1", "user2"]
organizations: ["org1", "org2"]
teams: ["org1/team1", "org2/team2"]
policy-bot
will attempt to request 2 reviewers randomly from the expanded
set of users of in
["user1", "user2", "users in org1", "users in org2", "users in org1/team1", "users in org2/team"]
Where the Pull Request Author and any non direct collaborators have been removed from the set.
While policy-bot
can be used to implement security controls on GitHub
repositories, there are important limitations to be aware of before adopting
this approach.
policy-bot
reports approval status to GitHub using commit statuses. While
statuses cannot be deleted, they can be set or overwritten by any user with
write access to a repository. To prevent forged statuses, GitHub allows setting
an expected source for a status check when making it a requirement on a
protected branch. Policy Bot always should be set as the expect source for
its checks.
For older versions of GitHub Enterprise that do not support expected sources
for status checks, policy-bot
contains an auditing feature to detect
overwritten statuses. In addition to logging an audit event, it will replace
the forged status with a failure. However, a well-timed attempt can still
approve and merge a pull request before policy-bot
can detect the problem.
Organizations concerned about this case should monitor and alert on the
relevant audit logs or minimize write access to repositories.
GitHub users with sufficient permissions can edit the comments of other users,
possibly changing an unrelated comment into one that enables approval.
policy-bot
also contains audting for this event, but as with statuses, a
well-timed edit can approve and merge a pull request before policy-bot
can
detect the problem. Organizations concerned about this case can use the
ignore_edited_comments
option or can monitor and alert on the relevant audit
logs.
This issue can also be minimized by only using GitHub reviews for approval, at the expense of removing the ability to self-approve pull requests.
GitHub associates commits with users by mapping the email address in a commit
to email addresses associated with GitHub user accounts. policy-bot
then uses
the GitHub username to evaluate user-based rules and options. There are two
failure modes in this process:
-
If GitHub does not recognize either the author or committer email of a commit,
policy-bot
cannot evaluate the commit with respect to user-based rules and the commit is effectively ignored. -
If emails are manipulated when creating a commit, a user can trick GitHub and
policy-bot
into attributing the commit to a different user.
If using GitHub Enterprise, both of these issues are avoidable by using the commit-current-user-check pre-receive hook.
When using the ignore_update_merges
option, policy-bot
cannot tell the
difference between clean merges and merges that contain conflict resolution.
This means that a user who carefully crafts a pull request to generate a
conflict can use the web conflict editor to add unapproved changes to the file
containing the conflict.
Depending on the author of the merge commits, it may be possible to avoid this
issue by using the ignore_commits_by
option in combination with the
commit-current-user-check pre-receive hook.
policy-bot
is easy to deploy in your own environment as it has no dependencies
other than GitHub. It is also safe to run multiple instances of the server,
making it a good fit for container schedulers like Nomad or Kubernetes.
We provide both a Docker container and a binary distribution of the server:
- Binaries: https://github.com/palantir/policy-bot/releases
- Docker Images: https://hub.docker.com/r/palantirtechnologies/policy-bot/
A sample configuration file is provided at config/policy-bot.example.yml
.
Certain values may also be set by environment variables; these are noted in the
comments in the sample configuration file.
To configure policy-bot
as a GitHub App, set these options in GitHub:
- Under Identifying and authorizing users
- Set User authorization callback URL to
http(s)://<your-policy-bot-domain>/api/github/auth
- Uncheck Request user authorization (OAuth) during installation
- Set User authorization callback URL to
- Under Webhook
- Set Webhook URL to
http(s)://<your-policy-bot-domain>/api/github/hook
- Set Webhook secret: A random string that matches the value of the
github.app.webhook_secret
property in the server configuration
- Set Webhook URL to
The app requires these permissions:
Permission | Access | Reason |
---|---|---|
Repository contents | Read-only | Read configuration and commit metadata |
Checks | Read-only | Read check run results |
Repository administration | Read-only | Read admin team(s) membership |
Issues | Read-only | Read pull request comments |
Repository metadata | Read-only | Basic repository data |
Pull requests | Read & write | Receive pull request events, read metadata. Assign reviewers |
Commit status | Read & write | Post commit statuses |
Organization members | Read-only | Determine organization and team membership |
The app should be subscribed to these events:
- Check run
- Issue comment
- Pull request
- Pull request review
- Status
There is a logo.png
provided if you'd like to use it as the GitHub application logo. The background
color is #4d4d4d
.
After creating the app, update the server configuration file with the following generated values:
- App ID (
github.app.integration_id
) - Client ID (
github.oauth.client_id
) - Client secret (
github.oauth.client_secret
) - Private key (
github.app.private_key
)
policy-bot
uses go-baseapp and
go-githubapp, both of which emit
standard metrics and structured log keys. Please see those projects for
details.
To develop policy-bot
, you will need a Go installation.
If you want to build the UI, you'll also need NodeJS
and Yarn.
Run style checks and tests
./godelw verify
Running the server locally
# copy and edit the server config
cp config/policy-bot.example.yml config/policy-bot.yml
./godelw run policy-bot server
config/policy-bot.yml
is used as the default configuration file- The server is available at
http://localhost:8080/
Installing UI dependencies and building assets
# install dependencies
yarn install
# build CSS and JS assets
yarn run build
-
This generates a combined stylesheet with
policy-bot
styles and Tailwind core styles. It also copies JS files and other assets into the correct locations. -
To use the local asset files with a local server, add or uncomment the following in the server configuration file:
files: static: build/static templates: server/templates
Running the server via docker
# copy and edit the server config
cp config/policy-bot.example.yml config/policy-bot.yml
# build the docker image
./godelw docker build --verbose
docker run --rm -v "$(pwd)/config:/secrets/" -p 8080:8080 palantirtechnologies/policy-bot:latest
- This will mount the path relative path
config/
which should contain the modified config filepolicy-bot.yml
- The server is available at
http://localhost:8080/
Example policy files can be found in config/policy-examples
Contributions and issues are welcome. For new features or large contributions, we prefer discussing the proposed change on a GitHub issue prior to a PR.
This library is made available under the Apache 2.0 License.