A feature-rich and robust Cloudflare DDNS updater with a small footprint. The program will detect your machineβs public IP addresses and update DNS records using the Cloudflare API.
- π€ The Docker image takes less than 5 MB after compression.
- π The Go runtime re-uses existing HTTP connections.
- ποΈ Cloudflare API responses are cached to reduce the API usage.
- π You can simply list domains (e.g.,
www.a.org, hello.io
) without knowing their DNS zones. - π Internationalized domain names (e.g.,
π±.example.org
andζ₯ζ¬ο½‘coqjp
) are fully supported. - π Wildcard domains (e.g.,
*.example.org
) are also supported. - πΉοΈ You can toggle IPv4 (
A
records) and IPv6 (AAAA
records) for each domain.
- πΆβπ«οΈ You can toggle Cloudflare proxying for each domain.
- π You can set comments for new DNS records.
- π The updater can maintain lists of detected IP addresses. These lists can then be referenced in any Cloudflare product that uses Cloudflareβs Rules language, such as Cloudflare Web Application Firewall (WAF) and Cloudflare Rules. (We call the lists βWAF listsβ, but their use is not limited to Cloudflare WAF.)
- π©Ί The updater can report to Healthchecks or Uptime Kuma so that you receive notifications when it fails to update IP addresses.
- π£ The updater can also actively update you via any service supported by the shoutrrr library, including emails, major notification services, major messaging platforms, and generic webhooks.
By default, public IP addresses are obtained via Cloudflareβs debugging page. This minimizes the impact on privacy because we are already using the Cloudflare API to update DNS records. Moreover, if Cloudflare servers are not reachable, chances are you cannot update DNS records anyways.
-
π‘οΈ The updater uses only HTTPS or DNS over HTTPS to detect IP addresses. This makes it harder for someone else to trick the updater into updating your DNS records with wrong IP addresses. See the Security Model for more information.
-
Click to expand: βοΈ You can verify the Docker images were built from this repository using the cosign tool.
cosign verify favonia/cloudflare-ddns:latest \ --certificate-identity-regexp https://github.com/favonia/cloudflare-ddns/ \ --certificate-oidc-issuer https://token.actions.githubusercontent.com
Note: this only proves that the Docker image is from this repository, assuming that no one hacks into GitHub or the repository. It does not prove that the code itself is secure.
-
Click to expand: π The updater uses only established open-source Go libraries.
- cloudflare-go:
The official Go binding of Cloudflare API v4. - cron:
Parsing of Cron expressions. - go-retryablehttp:
HTTP clients with automatic retries and exponential backoff. - go-querystring:
A library to construct URL query parameters. - shoutrrr:
A notification library for sending general updates. - ttlcache:
In-memory cache to hold Cloudflare API responses. - mock (for testing only):
A comprehensive, semi-official framework for mocking. - testify (for testing only):
A comprehensive tool set for testing Go programs.
- cloudflare-go:
Click to expand: π Directly run the Docker image
docker run \
--network host \
-e CLOUDFLARE_API_TOKEN=YOUR-CLOUDFLARE-API-TOKEN \
-e DOMAINS=example.org,www.example.org,example.io \
-e PROXIED=true \
favonia/cloudflare-ddns:latest
Click to expand: 𧬠Directly run the updater from its source
You need the Go tool to run the updater from its source.
CLOUDFLARE_API_TOKEN=YOUR-CLOUDFLARE-API-TOKEN \
DOMAINS=example.org,www.example.org,example.io \
PROXIED=true \
go run github.com/favonia/cloudflare-ddns/cmd/ddns@latest
See community-contributed sample configurations for OpenBSD.
Incorporate the following fragment into the compose file (typically docker-compose.yml
or docker-compose.yaml
). The template may look a bit scary, but only because it includes various optional flags for extra security protection.
services:
cloudflare-ddns:
image: favonia/cloudflare-ddns:latest
# Choose the appropriate tag based on your need:
# - "latest" for the latest stable version (which could become 2.x.y
# in the future and break things)
# - "1" for the latest stable version whose major version is 1
# - "1.x.y" to pin the specific version 1.x.y
network_mode: host
# This bypasses network isolation and makes IPv6 easier (optional; see below)
restart: always
# Restart the updater after reboot
user: "1000:1000"
# Run the updater with specific user and group IDs (in that order).
# You can change the two numbers based on your need.
read_only: true
# Make the container filesystem read-only (optional but recommended)
cap_drop: [all]
# Drop all Linux capabilities (optional but recommended)
security_opt: [no-new-privileges:true]
# Another protection to restrict superuser privileges (optional but recommended)
environment:
- CLOUDFLARE_API_TOKEN=YOUR-CLOUDFLARE-API-TOKEN
# Your Cloudflare API token
- DOMAINS=example.org,www.example.org,example.io
# Your domains (separated by commas)
- PROXIED=true
# Tell Cloudflare to cache webpages and hide your IP (optional)
Click to expand: π CLOUDFLARE_API_TOKEN
is your Cloudflare API token
The value of CLOUDFLARE_API_TOKEN
should be an API token (not an API key), which can be obtained from the API Tokens page. Use the Edit zone DNS template to create a token. The less secure API key authentication is deliberately not supported.
There is an optional feature (available since version 1.14.0) that lets you maintain a WAF list of detected IP addresses. To use this feature, edit the token and grant it the Account - Account Filter Lists - Edit permission. If you only need to update WAF lists, not DNS records, you can remove the Zone - DNS - Edit permission. Refer to the detailed documentation below for information on updating WAF lists.
Click to expand: π DOMAINS
is the list of domains to update
The value of DOMAINS
should be a list of fully qualified domain names (FQDNs) separated by commas. For example, DOMAINS=example.org,www.example.org,example.io
instructs the updater to manage the domains example.org
, www.example.org
, and example.io
. These domains do not have to share the same DNS zone---the updater will take care of the DNS zones behind the scene.
Click to expand: π¨ Remove PROXIED=true
if you are not running a web server
The setting PROXIED=true
instructs Cloudflare to cache webpages and hide your IP addresses. If you wish to bypass that and expose your actual IP addresses, remove PROXIED=true
. If your traffic is not HTTP(S), then Cloudflare cannot proxy it and you should probably turn off the proxying by removing PROXIED=true
. The default value of PROXIED
is false
.
Click to expand: π΄ Add IP6_PROVIDER=none
if you want to disable IPv6 completely
The updater, by default, will attempt to update DNS records for both IPv4 and IPv6, and there is no harm in leaving the automatic detection on even if your network does not work for one of them. However, if you want to disable IPv6 entirely (perhaps to avoid seeing the detection errors), add IP6_PROVIDER=none
.
Click to expand: π‘ Use IPv6 without bypassing network isolation (without network_mode: host
)
The easiest way to enable IPv6 is to use network_mode: host
so that the updater can access the host IPv6 network directly. This has the downside of bypassing the network isolation. If you wish to keep the updater isolated from the host network, remove network_mode: host
and follow the steps in the official Docker documentation to enable IPv6. Do use newer versions of Docker that come with much better IPv6 support!
Click to expand: π‘οΈ Change user: "1000:1000"
to the user and group IDs you want to use
Change 1000:1000
to USER:GROUP
for the USER
and GROUP
IDs you wish to use to run the updater. The settings cap_drop
, read_only
, and no-new-privileges
in the template provide additional protection, especially when you run the container as a non-superuser.
docker-compose pull cloudflare-ddns
docker-compose up --detach --build cloudflare-ddns
Click to expand: β I simulated an IP address change by editing the DNS records, but the updater never picked it up!
Please rest assured that the updater is working as expected. It will update the DNS records immediately for a real IP change. Here is a detailed explanation. There are two causes of an IP mismatch:
- A change of your actual IP address (a real change), or
- A change of the IP address in the DNS records (a simulated change).
The updater assumes no one will actively change the DNS records. In other words, it assumes simulated changes will not happen. It thus caches the DNS records and cannot detect your simulated changes. However, when your actual IP address changes, the updater will immediately update the DNS records. Also, the updater will eventually check the DNS records and detect simulated changes after CACHE_EXPIRATION
(six hours by default) has passed.
If you really wish to test the updater with simulated IP changes in the DNS records, you can set CACHE_EXPIRATION=1ns
(all cache expiring in one nanosecond), effectively disabling the caching. However, it is recommended to keep the default value (six hours) to reduce your network traffic.
Click to expand: β How can I see the timestamps of the IP checks and/or updates?
The updater does not itself add timestamps because all major systems already timestamp everything:
- If you are using Docker Compose, Kubernetes, or Docker directly, add the option
--timestamps
when viewing the logs. - If you are using Portainer, enable βShow timestampβ when viewing the logs.
Click to expand: β Why did the updater detect a public IP address different from the WAN IP address on my router?
Is your βpublicβ IP address on your router between 100.64.0.0
and 100.127.255.255
? If so, you are within your ISPβs CGNAT (Carrier-grade NAT). In practice, there is no way for DDNS to work with CGNAT, because your ISP does not give you a real public IP address, nor does it allow you to forward IP packages to your router using cool protocols such as Port Control Protocol. You have to give up DDNS or switch to another ISP. You may consider other services such as Cloudflare Tunnel that can work around CGNAT.
Click to expand: β How should I install this updater in βΈοΈ Kubernetes?
While the instructions for Kubernetes were removed due to high maintenance, you can still generate Kubernetes configurations from the provided Docker Compose template using a conversion tool like Kompose. Please note that only recent versions of Kompose support the user: "UID:GID"
attribute with GID
. (For more information, see my pull request that adds this feature to Kompose.)
Note that a simple Kubernetes Deployment will suffice here. Since thereβs no inbound network traffic, a Kubernetes Service isnβt required.
Click to expand: β Help! I got exec /bin/ddns: operation not permitted
Certain Docker installations may have issues with the no-new-privileges
security option. If you cannot run Docker images with this option (including this updater), removing it might be necessary. This will slightly compromise security, but itβs better than not running the updater at all. If only this updater is affected, please report this issue on GitHub.
Click to expand: β I am getting error code: 1034
We have received reports that the default IP provider, cloudflare.trace
, has recently begun returning an "error code: 1034." The current theory is that Cloudflareβs servers may be experiencing internal problems. We are tracking this issue at GitHub Issue 985. If IP detection fails, the updater will simply retry later. You can also switch to a different IP provider.
The emoji βπ§ͺβ indicates experimental features and the emoji βπ€β indicates technical details.
Click to expand: π The Cloudflare API token
Starting with version 1.15.0, the updater supports environment variables that begin with
CLOUDFLARE_*
. Multiple environment variables can be used at the same time, provided they all specify the same token.
Name | Meaning |
---|---|
CLOUDFLARE_API_TOKEN |
The Cloudflare API token to access the Cloudflare API |
CLOUDFLARE_API_TOKEN_FILE |
A path to a file that contains the Cloudflare API token to access the Cloudflare API |
CF_API_TOKEN (will be deprecated in version 2.0.0) |
Same as CLOUDFLARE_API_TOKEN |
CF_API_TOKEN_FILE (will be deprecated version in 2.0.0) |
Same as CLOUDFLARE_API_TOKEN_FILE |
π Cloudflare is updating its tools to use environment variables starting with
CLOUDFLARE_*
instead ofCF_*
. It is recommended to align your setting to align with this new convention. However, the updater will fully support bothCLOUDFLARE_*
andCF_*
environment variables until version 2.0.0.π To update DNS records, the updater needs the Zone - DNS - Edit permission.
π To manipulate WAF lists, the updater needs the Account - Account Filter Lists - Edit permission.
Click to expand: π DNS domains and WAF lists to update
You need to specify at least one thing in
DOMAINS
,IP4_DOMAINS
,IP6_DOMAINS
, or π§ͺWAF_LISTS
(since version 1.14.0) for the updater to update.
Name | Meaning |
---|---|
DOMAINS |
Comma-separated fully qualified domain names or wildcard domain names that the updater should manage for both A and AAAA records. Listing a domain in DOMAINS is equivalent to listing the same domain in both IP4_DOMAINS and IP6_DOMAINS . |
IP4_DOMAINS |
Comma-separated fully qualified domain names or wildcard domain names that the updater should manage for A records |
IP6_DOMAINS |
Comma-separated fully qualified domain names or wildcard domain names that the updater should manage for AAAA records |
π§ͺ WAF_LISTS (since version 1.14.0) |
π§ͺ Comma-separated references of WAF lists the updater should manage. A list reference is written in the format π The API token needs the Account - Account Filter Lists - Edit permission. |
ππ€ Wildcard domains (
*.example.org
) represent all subdomains that would not exist otherwise. Therefore, if you have another subdomain entrysub.example.org
, the wildcard domain is independent of it, because it only represents the other subdomains which do not have their own entries. Also, you can only have one layer of*
---*.*.example.org
would not work.
ππ€ Internationalized domain names are handled using the nontransitional processing (fully compatible with IDNA2008). At this point, all major browsers and whatnot have switched to the same nontransitional processing. See this useful FAQ on internationalized domain names.
π€ Technical notes on WAF lists:
- Cloudflare does not allow single IPv6 addresses in a WAF list, and thus the updater will use the smallest IP range allowed by Cloudflare that contains the detected IPv6 address.
- The updater will delete IP addresses belonging to unmanaged IP families from the specified WAF lists (e.g., if you disable IPv6 with
IP6_PROVIDER=none
, then existing IPv6 addresses or IPv6 ranges in the lists will be deleted). The idea is that the list should contain only detected IP addresses.
Click to expand: π IP address providers
Name | Meaning | Default Value |
---|---|---|
IP4_PROVIDER |
This specifies how to detect the current IPv4 address. Available providers include cloudflare.doh , cloudflare.trace , local , local.iface:<iface> , url:<URL> , and none . The special none provider disables IPv4 completely. See below for a detailed explanation. |
cloudflare.trace |
IP6_PROVIDER |
This specifies how to detect the current IPv6 address. Available providers include cloudflare.doh , cloudflare.trace , local , local.iface:<iface> , url:<URL> , and none . The special none provider disables IPv6 completely. See below for a detailed explanation. |
cloudflare.trace |
π The option
IP4_PROVIDER
governsA
-type DNS records and IPv4 addresses in WAF lists, while the optionIP6_PROVIDER
governsAAAA
-type DNS records and IPv6 addresses in WAF lists. The two options act independently of each other. You can specify different address providers for IPv4 and IPv6.
Provider Name | Explanation |
---|---|
cloudflare.doh |
Get the IP address by querying whoami.cloudflare. against Cloudflare via DNS-over-HTTPS. |
cloudflare.trace |
Get the IP address by parsing the Cloudflare debugging page. This is the default provider. |
local |
Get the IP address via local network interfaces and routing tables. The updater will use the local address that would have been used for outbound UDP connections to Cloudflare servers. (No data will be transmitted.)
|
π§ͺ local.iface:<iface> (available since version 1.15.0 but not finalized until 1.16.0) |
π§ͺ Get the IP address via the specific local network interface
|
url:<URL> |
Fetch the IP address from a URL. The provider format is url: followed by the URL itself. For example, IP4_PROVIDER=url:https://api4.ipify.org will fetch the IPv4 address from https://api4.ipify.org. Since version 1.15.0, the updater will enforce the matching protocol (IPv4 or IPv6) when connecting to the provided URL. Currently, only HTTP(S) is supported. |
none |
Stop the DNS updating for the specified IP version completely. For example π§ͺ The IP addresses of the disabled IP version will be removed from WAF lists; so |
Click to expand: π Scheduling of IP detections and updates
Name | Meaning | Default Value |
---|---|---|
CACHE_EXPIRATION |
The expiration of cached Cloudflare API responses. It can be any positive time duration accepted by time.ParseDuration, such as 1h or 10m . |
6h0m0s (6 hours) |
DELETE_ON_STOP |
Whether managed DNS records and WAF lists should be deleted on exit. It can be any boolean value accepted by strconv.ParseBool, such as true , false , 0 or 1 . If a WAF list is used in a rule expression, the list cannot be deleted (for otherwise the rule expression would be broken), but the updater will try to remove all IP addresses from the list. |
false |
TZ |
The timezone used for logging messages and parsing π€ The pre-built Docker images come with the embedded timezone database via the time/tzdata package. |
UTC |
UPDATE_CRON |
The schedule to re-check IP addresses and update DNS records and WAF lists (if needed). The format is any cron expression accepted by the π€ The update schedule does not take the time to update records into consideration. For example, if the schedule is |
@every 5m (every 5 minutes) |
UPDATE_ON_START |
Whether to check IP addresses (and possibly update DNS records and WAF lists) immediately on start, regardless of the update schedule specified by UPDATE_CRON . It can be any boolean value accepted by strconv.ParseBool, such as true , false , 0 or 1 . |
true |
Click to expand: β³ Timeouts of various operations
Name | Meaning | Default Value |
---|---|---|
DETECTION_TIMEOUT |
The timeout of each attempt to detect IP address, per IP version (IPv4 and IPv6). It can be any positive time duration accepted by time.ParseDuration, such as 1h or 10m . |
5s (5 seconds) |
UPDATE_TIMEOUT |
The timeout of each attempt to update DNS records, per domain and per record type, or per WAF list. It can be any positive time duration accepted by time.ParseDuration, such as 1h or 10m . |
30s (30 seconds) |
Click to expand: π£ Parameters of new DNS records and WAF lists (proxy status, TTL, and comments)
π The updater will preserve existing parameters (TTL, proxy statuses, DNS record comments, etc.). Only when it creates new DNS records and new WAF lists, the following settings will apply. To change existing parameters, you can go to your Cloudflare Dashboard and change them directly. If you think you have a use case where the updater should actively overwrite existing parameters in addition to IP addresses, please let me know. ππ§ͺ KNOWN ISSUE: comments of stale WAF list items (not WAF lists themselves) will not be kept because the Cloudflare API does not provide an easy way to update list items. The comments will be lost when the updater deletes stale list items and create new ones.
Name | Meaning | Default Value |
---|---|---|
PROXIED |
Whether new DNS records should be proxied by Cloudflare. It can be any boolean value accepted by strconv.ParseBool, such as π€ Advanced usage: it can also be a domain-dependent boolean expression as described below. |
false |
TTL |
The time-to-live (TTL) (in seconds) of new DNS records. | 1 (This means βautomaticβ to Cloudflare) |
RECORD_COMMENT |
The record comment of new DNS records. | "" |
π§ͺ WAF_LIST_DESCRIPTION (since version 1.14.0) |
π§ͺ The text description of new WAF lists. | "" |
π€ For advanced users: the
PROXIED
can be a boolean expression involving domains! This allows you to enable Cloudflare proxying for some domains but not the others. Here are some example expressions:
PROXIED=is(example.org)
: proxy only the domainexample.org
PROXIED=is(example1.org) || sub(example2.org)
: proxy only the domainexample1.org
and subdomains ofexample2.org
PROXIED=!is(example.org)
: proxy every managed domain except forexample.org
PROXIED=is(example1.org) || is(example2.org) || is(example3.org)
: proxy only the domainsexample1.org
,example2.org
, andexample3.org
A boolean expression must be one of the following forms (all whitespace is ignored):
Syntax Meaning Any string accepted by strconv.ParseBool, such as true
,false
,0
, or1
Logical truth or falsehood is(d)
Matching the domain d
. Note thatis(*.a)
only matches the wildcard domain*.a
; usesub(a)
to match all subdomains ofa
(including*.a
).sub(d)
Matching subdomains of d
, such asa.d
,b.c.d
, and*.d
. It does not match the domaind
itself.! e
Logical negation of the boolean expression e
e1 || e2
Logical disjunction of the boolean expressions e1
ande2
e1 && e2
Logical conjunction of the boolean expressions e1
ande2
One can use parentheses to group expressions, such as
!(is(a) && (is(b) || is(c)))
. For convenience, the parser also accepts these short forms:
Short Form Equivalent Full Form is(d1, d2, ..., dn)
is(d1) || is(d2) || ... || is(dn)
sub(d1, d2, ..., dn)
sub(d1) || sub(d2) || ... || sub(dn)
For example, these two settings are equivalent:
PROXIED=is(example1.org) || is(example2.org) || is(example3.org)
PROXIED=is(example1.org,example2.org,example3.org)
Click to expand: ποΈ Message logging options
Name | Meaning | Default Value |
---|---|---|
EMOJI |
Whether the updater should use emojis in the logging. It can be any boolean value accepted by strconv.ParseBool, such as true , false , 0 or 1 . |
true |
QUIET |
Whether the updater should reduce the logging. It can be any boolean value accepted by strconv.ParseBool, such as true , false , 0 or 1 . |
false |
Click to expand: π£ Notification services (Healthchecks, Uptime Kuma, and shoutrrr)
π‘ If your network doesnβt support IPv6, set
IP6_PROVIDER=none
to disable IPv6. This will prevent the updater from reporting failures in detecting IPv6 addresses to monitoring services. Similarly, setIP4_PROVIDER=none
if your network doesnβt support IPv4.
Name | Meaning |
---|---|
HEALTHCHECKS |
The Healthchecks ping URL to ping when the updater successfully updates IP addresses, such as
|
UPTIMEKUMA |
The Uptime Kumaβs Push URL to ping when the updater successfully updates IP addresses, such as
|
π§ͺ SHOUTRRR (since version 1.12.0) |
Newline-separated shoutrrr URLs to which the updater sends notifications of IP address changes and other events. Each shoutrrr URL represents a notification service; for example, discord://<token>@<id> means sending messages to Discord. |
If you are using Docker Compose, run docker-compose up --detach
to reload settings.
Click to expand: I am migrating from oznu/cloudflare-ddns (now archived)
Old Parameter | Note | |
---|---|---|
API_KEY=key |
βοΈ | Use CLOUDFLARE_API_TOKEN=key |
API_KEY_FILE=file |
βοΈ | Use CLOUDFLARE_API_TOKEN_FILE=file |
ZONE=example.org and SUBDOMAIN=sub |
βοΈ | Use DOMAINS=sub.example.org directly |
PROXIED=true |
βοΈ | Same (PROXIED=true ) |
RRTYPE=A |
βοΈ | Both IPv4 and IPv6 are enabled by default; use IP6_PROVIDER=none to disable IPv6 |
RRTYPE=AAAA |
βοΈ | Both IPv4 and IPv6 are enabled by default; use IP4_PROVIDER=none to disable IPv4 |
DELETE_ON_STOP=true |
βοΈ | Same (DELETE_ON_STOP=true ) |
INTERFACE=name |
βοΈ | To automatically select the local address, use IP4/6_PROVIDER=local . π§ͺ To select the first address of a specific network interface, use IP4/6_PROVIDER=local.iface:name (available since version 1.15.0 but not finalized until 1.16.0). |
CUSTOM_LOOKUP_CMD=cmd |
β | Custom commands are not supported because there are no other programs in the minimal Docker image |
DNS_SERVER=server |
β | The updater only supports secure DNS queries using Cloudflareβs DNS over HTTPS (DoH) server. To enable this, set IP4/6_PROVIDER=cloudflare.doh . |
Click to expand: I am migrating from timothymiller/cloudflare-ddns
Old JSON Key | Note | |
---|---|---|
cloudflare.authentication.api_token |
βοΈ | Use CLOUDFLARE_API_TOKEN=key |
cloudflare.authentication.api_key |
β | Please use the newer, more secure API tokens |
cloudflare.zone_id |
βοΈ | Not needed; automatically retrieved from the server |
cloudflare.subdomains[].name |
βοΈ | Use DOMAINS with fully qualified domain names (FQDNs) directly; for example, if your zone is example.org and your subdomain is sub , use DOMAINS=sub.example.org |
cloudflare.subdomains[].proxied |
βοΈ | Write boolean expressions for PROXIED to specify per-domain settings; see above for the detailed documentation for this advanced feature |
load_balancer |
β | Not supported yet; please make a request if you want it |
a |
βοΈ | Both IPv4 and IPv6 are enabled by default; use IP4_PROVIDER=none to disable IPv4 |
aaaa |
βοΈ | Both IPv4 and IPv6 are enabled by default; use IP6_PROVIDER=none to disable IPv6 |
proxied |
βοΈ | Use PROXIED=true or PROXIED=false |
purgeUnknownRecords |
β | The updater never deletes unmanaged DNS records |
π Some historical notes: This updater was originally written as a Go clone of the Python program timothymiller/cloudflare-ddns because the Python program always purged unmanaged DNS records back then and it was not configurable via environment variables. There were feature requests to address these issues but the author timothymiller seemed to ignore them; I thus made my Go clone after unsuccessful communications. Understandably, timothymiller did not seem happy with my cloning and my other critical comments towards other aspects of the Python updater. Eventually, an option
purgeUnknownRecords
was added to the Python program to disable the unwanted purging, and it became configurable via environment variables, but my Go clone already went on its way. I believe my Go clone is now a much better choice, but my opinions are biased and you should check the technical details by yourself. π
Questions, suggestions, feature requests, and contributions are all welcome! Feel free to open a GitHub issue.
The code is licensed under Apache 2.0 with LLVM exceptions. (The LLVM exceptions provide better compatibility with GPL 2.0 and other license exceptions.)