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# ACLs
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A key component of tailscale is the notion of Tailnet. This notion is hidden
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but the implications that it have on how to use tailscale are not.
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For tailscale an [tailnet](https://tailscale.com/kb/1136/tailnet/) is the
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following:
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> For personal users, you are a tailnet of many devices and one person. Each
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> device gets a private Tailscale IP address in the CGNAT range and every
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> device can talk directly to every other device, wherever they are on the
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> internet.
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>
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> For businesses and organizations, a tailnet is many devices and many users.
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> It can be based on your Microsoft Active Directory, your Google Workspace, a
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> GitHub organization, Okta tenancy, or other identity provider namespace. All
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> of the devices and users in your tailnet can be seen by the tailnet
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> administrators in the Tailscale admin console. There you can apply
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> tailnet-wide configuration, such as ACLs that affect visibility of devices
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> inside your tailnet, DNS settings, and more.
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## Current implementation and issues
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Currently in headscale, the namespaces are used both as tailnet and users. The
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issue is that if we want to use the ACL's we can't use both at the same time.
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Tailnet's cannot communicate with each others. So we can't have an ACL that
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authorize tailnet (namespace) A to talk to tailnet (namespace) B.
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We also can't write ACLs based on the users (namespaces in headscale) since all
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devices belong to the same user.
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With the current implementation the only ACL that we can user is to associate
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each headscale IP to a host manually then write the ACLs according to this
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manual mapping.
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```json
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{
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"hosts": {
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"host1": "100.64.0.1",
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"server": "100.64.0.2"
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},
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"acls": [
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{ "action": "accept", "users": ["host1"], "ports": ["host2:80,443"] }
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]
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}
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```
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While this works, it requires a lot of manual editing on the configuration and
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to keep track of all devices IP address.
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## Proposition for a next implementation
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In order to ease the use of ACL's we need to split the tailnet and users
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notion.
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A solution could be to consider a headscale server (in it's entirety) as a
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tailnet.
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For personal users the default behavior could either allow all communications
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between all namespaces (like tailscale) or disallow all communications between
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namespaces (current behavior).
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For businesses and organisations, viewing a headscale instance a single tailnet
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would allow users (namespace) to talk to each other with the ACLs. As described
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in tailscale's documentation [[1]], a server should be tagged and personal
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devices should be tied to a user. Translated in headscale's terms each user can
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have multiple devices and all those devices should be in the same namespace.
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The servers should be tagged and used as such.
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This implementation would render useless the sharing feature that is currently
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implemented since an ACL could do the same. Simplifying to only one user
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interface to do one thing is easier and less confusing for the users.
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To better suit the ACLs in this proposition, it's advised to consider that each
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namespaces belong to one person. This person can have multiple devices, they
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will all be considered as the same user in the ACLs. OIDC feature wouldn't need
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to map people to namespace, just create a namespace if the person isn't
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registered yet.
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As a sidenote, users would like to write ACLs as YAML. We should offer users
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the ability to rules in either format (HuJSON or YAML).
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[1]: https://tailscale.com/kb/1068/acl-tags/
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## Example
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Let's build an example use case for a small business (It may be the place where
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ACL's are the most useful).
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We have a small company with a boss, an admin, two developer and an intern.
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The boss should have access to all servers but not to the users hosts. Admin
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should also have access to all hosts except that their permissions should be
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limited to maintaining the hosts (for example purposes). The developers can do
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anything they want on dev hosts, but only watch on productions hosts. Intern
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can only interact with the development servers.
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Each user have at least a device connected to the network and we have some
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servers.
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- database.prod
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- database.dev
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- app-server1.prod
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- app-server1.dev
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- billing.internal
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### Current headscale implementation
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Let's create some namespaces
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```bash
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headscale namespaces create prod
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headscale namespaces create dev
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headscale namespaces create internal
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headscale namespaces create users
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headscale nodes register -n users boss-computer
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headscale nodes register -n users admin1-computer
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headscale nodes register -n users dev1-computer
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headscale nodes register -n users dev1-phone
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headscale nodes register -n users dev2-computer
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headscale nodes register -n users intern1-computer
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headscale nodes register -n prod database
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headscale nodes register -n prod app-server1
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headscale nodes register -n dev database
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headscale nodes register -n dev app-server1
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headscale nodes register -n internal billing
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headscale nodes list
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ID | Name | Namespace | IP address
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1 | boss-computer | users | 100.64.0.1
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2 | admin1-computer | users | 100.64.0.2
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3 | dev1-computer | users | 100.64.0.3
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4 | dev1-phone | users | 100.64.0.4
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5 | dev2-computer | users | 100.64.0.5
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6 | intern1-computer | users | 100.64.0.6
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7 | database | prod | 100.64.0.7
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8 | app-server1 | prod | 100.64.0.8
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9 | database | dev | 100.64.0.9
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10 | app-server1 | dev | 100.64.0.10
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11 | internal | internal | 100.64.0.11
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```
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In order to only allow the communications related to our description above we
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need to add the following ACLs
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```json
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{
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"hosts": {
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"boss-computer": "100.64.0.1",
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"admin1-computer": "100.64.0.2",
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"dev1-computer": "100.64.0.3",
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"dev1-phone": "100.64.0.4",
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"dev2-computer": "100.64.0.5",
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"intern1-computer": "100.64.0.6",
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"prod-app-server1": "100.64.0.8"
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},
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"groups": {
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"group:dev": ["dev1-computer", "dev1-phone", "dev2-computer"],
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"group:admin": ["admin1-computer"],
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"group:boss": ["boss-computer"],
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"group:intern": ["intern1-computer"]
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},
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"acls": [
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// boss have access to all servers but no users hosts
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{
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"action": "accept",
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"users": ["group:boss"],
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"ports": ["prod:*", "dev:*", "internal:*"]
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},
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// admin have access to administration port (lets only consider port 22 here)
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{
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"action": "accept",
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"users": ["group:admin"],
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"ports": ["prod:22", "dev:22", "internal:22"]
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},
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// dev can do anything on dev servers and check access on prod servers
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{
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"action": "accept",
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"users": ["group:dev"],
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"ports": ["dev:*", "prod-app-server1:80,443"]
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},
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// interns only have access to port 80 and 443 on dev servers (lame internship)
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{ "action": "accept", "users": ["group:intern"], "ports": ["dev:80,443"] },
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// users can access their own devices
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{
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"action": "accept",
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"users": ["dev1-computer"],
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"ports": ["dev1-phone:*"]
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},
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{
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"action": "accept",
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"users": ["dev1-phone"],
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"ports": ["dev1-computer:*"]
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},
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// internal namespace communications should still be allowed within the namespace
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{ "action": "accept", "users": ["dev"], "ports": ["dev:*"] },
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{ "action": "accept", "users": ["prod"], "ports": ["prod:*"] },
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{ "action": "accept", "users": ["internal"], "ports": ["internal:*"] }
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]
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}
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```
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Since communications between namespace isn't possible we also have to share the
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devices between the namespaces.
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```bash
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// add boss host to prod, dev and internal network
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headscale nodes share -i 1 -n prod
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headscale nodes share -i 1 -n dev
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headscale nodes share -i 1 -n internal
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// add admin computer to prod, dev and internal network
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headscale nodes share -i 2 -n prod
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headscale nodes share -i 2 -n dev
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headscale nodes share -i 2 -n internal
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// add all dev to prod and dev network
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headscale nodes share -i 3 -n dev
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headscale nodes share -i 4 -n dev
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headscale nodes share -i 3 -n prod
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headscale nodes share -i 4 -n prod
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headscale nodes share -i 5 -n dev
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headscale nodes share -i 5 -n prod
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headscale nodes share -i 6 -n dev
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```
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This fake network have not been tested but it should work. Operating it could
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be quite tedious if the company grows. Each time a new user join we have to add
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it to a group, and share it to the correct namespaces. If the user want
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multiple devices we have to allow communication to each of them one by one. If
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business conduct a change in the organisations we may have to rewrite all acls
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and reorganise all namespaces.
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If we add servers in production we should also update the ACLs to allow dev
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access to certain category of them (only app servers for example).
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### example based on the proposition in this document
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Let's create the namespaces
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```bash
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headscale namespaces create boss
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headscale namespaces create admin1
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headscale namespaces create dev1
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headscale namespaces create dev2
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headscale namespaces create intern1
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```
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We don't need to create namespaces for the servers because the servers will be
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tagged. When registering the servers we will need to add the flag
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`--advertised-tags=tag:<tag1>,tag:<tag2>`, and the user (namespace) that is
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registering the server should be allowed to do it. Since anyone can add tags to
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a server they can register, the check of the tags is done on headscale server
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and only valid tags are applied. A tag is valid if the namespace that is
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registering it is allowed to do it.
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Here are the ACL's to implement the same permissions as above:
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```json
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{
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// groups are simpler and only list the namespaces name
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"groups": {
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"group:boss": ["boss"],
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"group:dev": ["dev1", "dev2"],
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"group:admin": ["admin1"],
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"group:intern": ["intern1"]
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},
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"tagOwners": {
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// the administrators can add servers in production
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"tag:prod-databases": ["group:admin"],
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"tag:prod-app-servers": ["group:admin"],
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// the boss can tag any server as internal
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"tag:internal": ["group:boss"],
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// dev can add servers for dev purposes as well as admins
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"tag:dev-databases": ["group:admin", "group:dev"],
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"tag:dev-app-servers": ["group:admin", "group:dev"]
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// interns cannot add servers
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},
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"acls": [
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// boss have access to all servers
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{
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"action": "accept",
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"users": ["group:boss"],
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"ports": [
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"tag:prod-databases:*",
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"tag:prod-app-servers:*",
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"tag:internal:*",
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"tag:dev-databases:*",
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"tag:dev-app-servers:*"
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]
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},
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// admin have only access to administrative ports of the servers
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{
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"action": "accept",
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"users": ["group:admin"],
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"ports": [
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"tag:prod-databases:22",
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"tag:prod-app-servers:22",
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"tag:internal:22",
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"tag:dev-databases:22",
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"tag:dev-app-servers:22"
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]
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},
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{
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"action": "accept",
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"users": ["group:dev"],
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"ports": [
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"tag:dev-databases:*",
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"tag:dev-app-servers:*",
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"tag:prod-app-servers:80,443"
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]
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},
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// servers should be able to talk to database. Database should not be able to initiate connections to server
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{
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"action": "accept",
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"users": ["tag:dev-app-servers"],
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"ports": ["tag:dev-databases:5432"]
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},
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{
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"action": "accept",
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"users": ["tag:prod-app-servers"],
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"ports": ["tag:prod-databases:5432"]
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},
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// interns have access to dev-app-servers only in reading mode
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{
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"action": "accept",
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"users": ["group:intern"],
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"ports": ["tag:dev-app-servers:80,443"]
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},
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// we still have to allow internal namespaces communications since nothing guarantees that each user have their own namespaces. This could be talked over.
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{ "action": "accept", "users": ["boss"], "ports": ["boss:*"] },
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{ "action": "accept", "users": ["dev1"], "ports": ["dev1:*"] },
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{ "action": "accept", "users": ["dev2"], "ports": ["dev2:*"] },
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{ "action": "accept", "users": ["admin1"], "ports": ["admin1:*"] },
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{ "action": "accept", "users": ["intern1"], "ports": ["intern1:*"] }
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]
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}
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```
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With this implementation, the sharing step is not necessary. Maintenance cost
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of the ACL file is lower and less tedious (no need to map hostname and IP's
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into it).
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@ -1,48 +0,0 @@
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# Better route management
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As of today, route management in Headscale is very basic and does not allow for much flexibility, including implementing subnet HA, 4via6 or more advanced features. We also have a number of bugs (e.g., routes exposed by ephemeral nodes)
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This proposal aims to improve the route management.
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## Current situation
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Routes advertised by the nodes are read from the Hostinfo struct. If approved from the the CLI or via autoApprovers, the route is added to the EnabledRoutes field in `Machine`.
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This means that the advertised routes are not persisted in the database, as Hostinfo is always replaced. In the same way, EnabledRoutes can get out of sync with the actual routes in the node.
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In case of colliding routes (i.e., subnets that are exposed from multiple nodes), we are currently just sending all of them in `PrimaryRoutes`... and hope for the best. (`PrimaryRoutes` is the field in `Node` used for subnet failover).
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## Proposal
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The core part is to create a new `Route` struct (and DB table), with the following fields:
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```go
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type Route struct {
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ID uint64 `gorm:"primary_key"`
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Machine *Machine
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Prefix IPPrefix
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Advertised bool
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Enabled bool
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IsPrimary bool
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CreatedAt *time.Time
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UpdatedAt *time.Time
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DeletedAt *time.Time
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}
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```
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- The `Advertised` field is set to true if the route is being advertised by the node. It is set to false if the route is removed. This way we can indicate if a later enabled route has stopped being advertised. A similar behaviour happens in the Tailscale.com control panel.
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- The `Enabled` field is set to true if the route is enabled - via CLI or autoApprovers.
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- `IsPrimary` indicates if Headscale has selected this route as the primary route for that particular subnet. This allows us to implement subnet failover. This would be fully automatic if there is more than subnet routers advertising the same network - which is the behaviour of Tailscale.com.
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## Stuff to bear in mind
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- We need to make sure to migrate the current `EnabledRoutes` of `Machine` into the new table.
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- When a node stops sharing a subnet, I reckon we should mark it both as not `Advertised` and not `Enabled`. Users should re-enable it if the node advertises it again.
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- If only one subnet router is advertising a subnet, we should mark it as primary.
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- Regarding subnet failover, the current behaviour of Tailscale.com is to perform the failover after 15 seconds from the node disconnecting from their control panel. I reckon we cannot do the same currently. Our maximum granularity is the keep alive period.
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@ -141,6 +141,3 @@ nav:
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- Android: android-client.md
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- Windows: windows-client.md
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- iOS: iOS-client.md
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- Proposals:
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- ACLs: proposals/001-acls.md
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- Better routing: proposals/002-better-routing.md
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Loading…
Reference in New Issue
Block a user