184 lines
7.2 KiB
Markdown
184 lines
7.2 KiB
Markdown
---
|
|
layout: "docs"
|
|
page_title: "Connect - Intentions"
|
|
sidebar_current: "docs-connect-intentions"
|
|
description: |-
|
|
Intentions define access control for services via Connect and are used to control which services may establish connections. Intentions can be managed via the API, CLI, or UI.
|
|
---
|
|
|
|
# Intentions
|
|
|
|
Intentions define access control for services via Connect and are used
|
|
to control which services may establish connections. Intentions can be
|
|
managed via the API, CLI, or UI.
|
|
|
|
Intentions are enforced by the [proxy](/docs/connect/proxies.html)
|
|
or [natively integrated application](/docs/connect/native.html) on
|
|
inbound connections. After verifying the TLS client certificate, the
|
|
[authorize API endpoint](#) is called which verifies the connection
|
|
is allowed by testing the intentions. If authorize returns false the
|
|
connection must be terminated.
|
|
|
|
The default intention behavior is defined by the default
|
|
[ACL policy](https://learn.hashicorp.com/consul/security-networking/production-acls). If the default ACL policy is "allow all",
|
|
then all Connect connections are allowed by default. If the default ACL policy
|
|
is "deny all", then all Connect connections are denied by default.
|
|
|
|
## Intention Basics
|
|
|
|
Intentions can be managed via the
|
|
[API](#),
|
|
[CLI](#),
|
|
or UI. Please see the respective documentation for each for full details
|
|
on options, flags, etc.
|
|
Below is an example of a basic intention to show the basic attributes
|
|
of an intention. The full data model of an intention can be found in the
|
|
[API documentation](#).
|
|
|
|
```
|
|
$ consul intention create -deny web db
|
|
Created: web => db (deny)
|
|
```
|
|
|
|
The intention above is a deny intention with a source of "web" and
|
|
destination of "db". This says that connections from web to db are not
|
|
allowed and the connection will be rejected.
|
|
|
|
When an intention is modified, existing connections will not be affected.
|
|
This means that changing a connection from "allow" to "deny" today
|
|
_will not_ kill the connection. Addressing this shortcoming is on
|
|
the near term roadmap for Consul.
|
|
|
|
### Wildcard Intentions
|
|
|
|
An intention source or destination may also be the special wildcard
|
|
value `*`. This matches _any_ value and is used as a catch-all. Example:
|
|
|
|
```
|
|
$ consul intention create -deny web '*'
|
|
Created: web => * (deny)
|
|
```
|
|
|
|
This example says that the "web" service cannot connect to _any_ service.
|
|
|
|
### Metadata
|
|
|
|
Arbitrary string key/value data may be associated with intentions. This
|
|
is unused by Consul but can be used by external systems or for visibility
|
|
in the UI.
|
|
|
|
```
|
|
$ consul intention create \
|
|
-deny \
|
|
-meta description='Hello there' \
|
|
web db
|
|
...
|
|
|
|
$ consul intention get web db
|
|
Source: web
|
|
Destination: db
|
|
Action: deny
|
|
ID: 31449e02-c787-f7f4-aa92-72b5d9b0d9ec
|
|
Meta[description]: Hello there
|
|
Created At: Friday, 25-May-18 02:07:51 CEST
|
|
```
|
|
|
|
## Precedence and Match Order
|
|
|
|
Intentions are matched in an implicit order based on specificity, preferring
|
|
deny over allow. Specificity is determined by whether a value is an exact
|
|
specified value or is the wildcard value `*`.
|
|
The full precedence table is shown below and is evaluated
|
|
top to bottom, with larger numbers being evaluated first.
|
|
|
|
| Source Name | Destination Name | Precedence |
|
|
| ----------- | ---------------- | ---------- |
|
|
| Exact | Exact | 9 |
|
|
| `*` | Exact | 8 |
|
|
| Exact | `*` | 6 |
|
|
| `*` | `*` | 5 |
|
|
|
|
The precedence value can be read from the [API](/api/connect/intentions.html)
|
|
after an intention is created.
|
|
Precedence cannot be manually overridden today. This is a feature that will
|
|
be added in a later version of Consul.
|
|
|
|
In the case the two precedence values match, Consul will evaluate
|
|
intentions based on lexographical ordering of the destination then
|
|
source name. In practice, this is a moot point since authorizing a connection
|
|
has an exact source and destination value so its impossible for two
|
|
valid non-wildcard intentions to match.
|
|
|
|
The numbers in the table above are not stable. Their ordering will remain
|
|
fixed but the actual number values may change in the future.
|
|
The numbers are non-contiguous because there are
|
|
some unused values in the middle in preparation for a future version of
|
|
Consul supporting namespaces.
|
|
|
|
## Intention Management Permissions
|
|
|
|
Intention management can be protected by [ACLs](https://learn.hashicorp.com/consul/security-networking/production-acls).
|
|
Permissions for intentions are _destination-oriented_, meaning the ACLs
|
|
for managing intentions are looked up based on the destination value
|
|
of the intention, not the source.
|
|
|
|
Intention permissions are by default implicitly granted at `read` level
|
|
when granting `service:read` or `service:write`. This is because a
|
|
service registered that wants to use Connect needs `intentions:read`
|
|
for its own service name in order to know whether or not to authorize
|
|
connections. The following ACL policy will implicitly grant `intentions:read`
|
|
(note _read_) for service `web`.
|
|
|
|
```hcl
|
|
service "web" {
|
|
policy = "write"
|
|
}
|
|
```
|
|
|
|
It is possible to explicitly specify intention permissions. For example,
|
|
the following policy will allow a service to be discovered without granting
|
|
access to read intentions for it.
|
|
|
|
```hcl
|
|
service "web" {
|
|
policy = "read"
|
|
intentions = "deny"
|
|
}
|
|
```
|
|
|
|
Note that `intentions:read` is required for a token that a Connect-enabled
|
|
service uses to register itself or it's proxy. If the token used does not
|
|
have `intentions:read` then the agent will be unable to resolve intentions
|
|
for the service and so will not be able to authorize any incoming connections.
|
|
|
|
~> **Security Note:** Explicitly allowing `intentions:write` on the token you
|
|
provide to a service instance at registration time opens up a significant
|
|
additional vulnerability. Although you may trust the service _team_ to define
|
|
which inbound connections they accept, using a combined token for registration
|
|
allows a compromised instance to to redefine the intentions which allows many
|
|
additional attack vectors and may be hard to detect. We strongly recommend only
|
|
delegating `intentions:write` using tokens that are used by operations teams or
|
|
orchestrators rather than spread via application config, or only manage
|
|
intentions with management tokens.
|
|
|
|
## Performance and Intention Updates
|
|
|
|
The intentions for services registered with a Consul agent are cached
|
|
locally on that agent. They are then updated via a background blocking query
|
|
against the Consul servers.
|
|
|
|
Connect connection attempts require only local agent
|
|
communication for authorization and generally impose only impose microseconds
|
|
of latency to the connection. All actions in the data path of connections
|
|
require only local data to ensure minimal performance overhead.
|
|
|
|
Updates to intentions are propagated nearly instantly to agents since agents
|
|
maintain a continuous blocking query in the background for intention updates
|
|
for registered services.
|
|
|
|
Because all the intention data is cached locally, the agents can fail static.
|
|
Even if the agents are severed completely from the Consul servers, inbound
|
|
connection authorization continues to work for a configured amount of time.
|
|
Changes to intentions will not be picked up until the partition heals, but
|
|
will then automatically take effect when connectivity is restored.
|