Merge pull request #500 from d3xf/pr-minor-doc-fixes

Minor documentation fixes
This commit is contained in:
Seth Vargo 2014-11-26 09:08:45 -05:00
commit 7a5b83bf24
14 changed files with 92 additions and 90 deletions

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@ -72,7 +72,7 @@ There are several important components that `consul agent` outputs:
agent. This is also the address other applications can use over [RPC to control Consul](/docs/agent/rpc.html).
* **Cluster Addr**: This is the address and ports used for communication between
Consul agents in a cluster. Every Consul agent in a cluster does not have to
Consul agents in a cluster. Not all Consul agents in a cluster have to
use the same port, but this address **MUST** be reachable by all other nodes.
## Stopping an Agent
@ -105,7 +105,7 @@ this lifecycle is useful to building a mental model of an agent's interactions
with a cluster, and how the cluster treats a node.
When an agent is first started, it does not know about any other node in the cluster.
To discover it's peers, it must _join_ the cluster. This is done with the `join`
To discover its peers, it must _join_ the cluster. This is done with the `join`
command or by providing the proper configuration to auto-join on start. Once a node
joins, this information is gossiped to the entire cluster, meaning all nodes will
eventually be aware of each other. If the agent is a server, existing servers will
@ -115,18 +115,18 @@ In the case of a network failure, some nodes may be unreachable by other nodes.
In this case, unreachable nodes are marked as _failed_. It is impossible to distinguish
between a network failure and an agent crash, so both cases are handled the same.
Once a node is marked as failed, this information is updated in the service catalog.
There is some nuance here relating, since this update is only possible if the
servers can still [form a quorum](/docs/internals/consensus.html). Once the network
failure recovers, or a crashed agent restarts, the cluster will repair itself,
and unmark a node as failed. The health check in the catalog will also be updated
to reflect this.
There is some nuance here since this update is only possible if the servers can
still [form a quorum](/docs/internals/consensus.html). Once the network recovers,
or a crashed agent restarts, the cluster will repair itself, and unmark
a node as failed. The health check in the catalog will also be updated to reflect
this.
When a node _leaves_, it specifies it's intent to do so, and so the cluster
When a node _leaves_, it specifies its intent to do so, and so the cluster
marks that node as having _left_. Unlike the _failed_ case, all of the
services provided by a node are immediately deregistered. If the agent was
a server, replication to it will stop. To prevent an accumulation
of dead nodes, Consul will automatically reap _failed_ nodes out of the
catalog as well. This is currently done on a non-configurable interval
which defaults to 72 hours. Reaping is similar to leaving, causing all
associated services to be deregistered.
catalog as well. This is currently done on a non-configurable interval of
72 hours. Reaping is similar to leaving, causing all associated services
to be deregistered.

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@ -16,12 +16,12 @@ or added at runtime over the HTTP interface.
There are two different kinds of checks:
* Script + Interval - These checks depend on invoking an external application
which does the health check and exits with an appropriate exit code, potentially
that does the health check and exits with an appropriate exit code, potentially
generating some output. A script is paired with an invocation interval (e.g.
every 30 seconds). This is similar to the Nagios plugin system.
* TTL - These checks retain their last known state for a given TTL. The state
of the check must be updated periodically over the HTTP interface. If an
* Time to Live (TTL) - These checks retain their last known state for a given TTL.
The state of the check must be updated periodically over the HTTP interface. If an
external system fails to update the status within a given TTL, the check is
set to the failed state. This mechanism is used to allow an application to
directly report its health. For example, a web app can periodically curl the
@ -75,7 +75,7 @@ check can be registered dynamically using the [HTTP API](/docs/agent/http.html).
## Check Scripts
A check script is generally free to do anything to determine the status
of the check. The only limitations placed are the exit codes must convey
of the check. The only limitations placed are that the exit codes must convey
a specific meaning. Specifically:
* Exit code 0 - Check is passing

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@ -8,22 +8,23 @@ description: |-
# DNS Interface
One of the primary query interfaces for Consul is using DNS.
One of the primary query interfaces for Consul is DNS.
The DNS interface allows applications to make use of service
discovery without any high-touch integration with Consul. For
example, instead of making any HTTP API requests to Consul,
example, instead of making HTTP API requests to Consul,
a host can use the DNS server directly and just do a name lookup
for "redis.service.east-aws.consul".
This query automatically translates to a lookup of nodes that
provide the redis service, located in the "east-aws" datacenter,
with no failing health checks. It's that simple!
provide the redis service, are located in the "east-aws" datacenter,
and have no failing health checks. It's that simple!
There are a number of [configuration options](/docs/agent/options.html) that
are important for the DNS interface. They are `client_addr`, `ports.dns`, `recursors`,
`domain`, and `dns_config`. By default Consul will listen on 127.0.0.1:8600 for DNS queries
in the "consul." domain, without support for DNS recursion. All queries are case-insensitive, a
name lookup for `PostgreSQL.node.dc1.consul` will find all nodes named `postgresql`, no matter of case.
in the "consul." domain, without support for DNS recursion. All queries are case-insensitive: a
name lookup for `PostgreSQL.node.dc1.consul` will find all nodes named `postgresql`,
regardless of case.
There are a few ways to use the DNS interface. One option is to use a custom
DNS resolver library and point it at Consul. Another option is to set Consul
@ -76,24 +77,24 @@ consul. 0 IN SOA ns.consul. postmaster.consul. 1392836399 3600 600 86400 0
## Service Lookups
A service lookup is the alternate type of query. It is used to query for service
providers and supports two mode of lookup, a strict RCF style lookup and the
standard lookup.
providers and supports two lookup methods: standard lookup, and strict
[RFC 2782](https://tools.ietf.org/html/rfc2782) lookup.
### Standard Style Lookup
### Standard Lookup
The format of a standard service lookup is like the following:
The format of a standard service lookup is:
[tag.]<service>.service[.datacenter][.domain]
As with node lookups, the `datacenter` is optional, as is the `tag`. If no tag is
provided, then no filtering is done on tag. So, if we want to find any redis service
providers in our local datacenter, we could lookup "redis.service.consul.", however
providers in our local datacenter, we could lookup "redis.service.consul.", while
if we care about the PostgreSQL master in a particular datacenter, we could lookup
"master.postgresql.service.dc2.consul."
The DNS query system makes use of health check information to prevent routing
to unhealthy nodes. When a service query is made, any services failing their health
check, or failing a node system check will be omitted from the results. To allow
check, or failing a node system check, will be omitted from the results. To allow
for simple load balancing, the set of nodes returned is also randomized each time.
These simple mechanisms make it easy to use DNS along with application level retries
as a simple foundation for an auto-healing service oriented architecture.
@ -124,13 +125,13 @@ consul.service.consul. 0 IN SRV 1 1 8300 foobar.node.dc1.consul.
foobar.node.dc1.consul. 0 IN A 10.1.10.12
```
### RFC-2782 Style Lookup
### RFC 2782 Lookup
The format for RFC style lookups uses the following format:
The format for RFC 2782 SRV lookups is:
_<service>._<protocol>.service[.datacenter][.domain]
Per [RFC-2782](https://www.ietf.org/rfc/rfc2782.txt), SRV queries should use
Per [RFC 2782](https://tools.ietf.org/html/rfc2782), SRV queries should use
underscores (_) as a prefix to the `service` and `protocol` values in a query to
prevent DNS collisions. The `protocol` value can be any of the tags for a
service or if the service has no tags, the value "tcp" should be used. If "tcp"
@ -139,7 +140,7 @@ is specified as the protocol, the query will not perform any tag filtering.
Other than the query format and default "tcp" protocol/tag value, the behavior
of the RFC style lookup is the same as the standard style of lookup.
Using the RCF style lookup, If you registered the service "rabbitmq" on port
Using RFC 2782 lookup, If you registered the service "rabbitmq" on port
5672 and tagged it with "amqp" you would query the SRV record as
"_rabbitmq._amqp.service.consul" as illustrated in the example below:
@ -168,7 +169,7 @@ rabbitmq.node1.dc1.consul. 0 IN A 10.1.11.20
When the DNS query is performed using UDP, Consul will truncate the results
without setting the truncate bit. This is to prevent a redundant lookup over
TCP which generate additional load. If the lookup is done over TCP, the results
TCP that generates additional load. If the lookup is done over TCP, the results
are not truncated.
## Caching

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@ -15,7 +15,7 @@ executable. As an example, you could watch the status of health checks and
notify an external system when a check is critical.
Watches are implemented using blocking queries in the [HTTP API](/docs/agent/http.html).
Agent's automatically make the proper API calls to watch for changes,
Agents automatically make the proper API calls to watch for changes,
and inform a handler when the data view has updated.
Watches can be configured as part of the [agent's configuration](/docs/agent/options.html),
@ -36,7 +36,7 @@ The watch specification specifies the view of data to be monitored.
Once that view is updated the specified handler is invoked. The handler
can be any executable.
A handler should read it's input from stdin, and expect to read
A handler should read its input from stdin, and expect to read
JSON formatted data. The format of the data depends on the type of the
watch. Each watch type documents the format type, and because they
map directly to an HTTP API, handlers should expect the input to
@ -280,7 +280,7 @@ An example of the output of this command:
### Type: checks
The "checks" watch type is used to monitor the checks of a given
service or in a specific state. It optionally takes the "service"
service or those in a specific state. It optionally takes the "service"
parameter to filter to a specific service, or "state" to filter
to a specific state. By default, it will watch all checks.

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@ -10,8 +10,8 @@ description: |-
We expect Consul to run in large clusters as long-running agents. Because
upgrading agents in this sort of environment relies heavily on protocol
compatibility, this page makes it clear on our promise to keeping different
Consul versions compatible with each other.
compatibility, this page makes clear our promise to keep different Consul
versions compatible with each other.
We promise that every subsequent release of Consul will remain backwards
compatible with _at least_ one prior version. Concretely: version 0.5 can

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@ -11,7 +11,7 @@ description: |-
Consul provides an optional Access Control List (ACL) system which can be used to control
access to data and APIs. The ACL system is a
[Capability-based system](http://en.wikipedia.org/wiki/Capability-based_security) that relies
on tokens which can have fine grained rules applied to them. It is very similar to
on tokens to which fine grained rules can be applied. It is very similar to
[AWS IAM](http://aws.amazon.com/iam/) in many ways.
## ACL Design
@ -30,10 +30,10 @@ perform all actions.
The token ID is passed along with each RPC request to the servers. Agents
[can be configured](/docs/agent/options.html) with `acl_token` to provide a default token,
but the token can also be specified by a client on a [per-request basis](/docs/agent/http.html).
ACLs are new as of Consul 0.4, meaning versions prior do not provide a token.
ACLs are new as of Consul 0.4, meaning prior versions do not provide a token.
This is handled by the special "anonymous" token. Anytime there is no token provided,
the rules defined by that token are automatically applied. This lets policy be enforced
on legacy clients.
the rules defined by that token are automatically applied. This allows
policy to be enforced on legacy clients.
Enforcement is always done by the server nodes. All servers must be [configured
to provide](/docs/agent/options.html) an `acl_datacenter`, which enables
@ -47,7 +47,7 @@ all the tokens.
When a request is made to any non-authoritative server with a token, it must
be resolved into the appropriate policy. This is done by reading the token
from the authoritative server and caching a configurable `acl_ttl`. The implication
of caching is that the cache TTL is an upper-bound on the staleness of policy
of caching is that the cache TTL is an upper bound on the staleness of policy
that is enforced. It is possible to set a zero TTL, but this has adverse
performance impacts, as every request requires refreshing the policy.

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@ -23,20 +23,20 @@ Before describing the architecture, we provide a glossary of terms to help
clarify what is being discussed:
* Agent - An agent is the long running daemon on every member of the Consul cluster.
It is started by running `consul agent`. The agent is able to run in either *client*,
It is started by running `consul agent`. The agent is able to run in either *client*
or *server* mode. Since all nodes must be running an agent, it is simpler to refer to
the node as either being a client or server, but there are other instances of the agent. All
the node as being either a client or server, but there are other instances of the agent. All
agents can run the DNS or HTTP interfaces, and are responsible for running checks and
keeping services in sync.
* Client - A client is an agent that forwards all RPCs to a server. The client is relatively
stateless. The only background activity a client performs is taking part of LAN gossip pool.
This has a minimal resource overhead and consumes only a small amount of network bandwidth.
stateless. The only background activity a client performs is taking part in the LAN gossip
pool. This has a minimal resource overhead and consumes only a small amount of network
bandwidth.
* Server - An agent that is server mode. When in server mode, there is an expanded set
of responsibilities including participating in the Raft quorum, maintaining cluster state,
responding to RPC queries, WAN gossip to other datacenters, and forwarding queries to leaders
or remote datacenters.
* Server - A server is an agent with an expanded set of responsibilities including
participating in the Raft quorum, maintaining cluster state, responding to RPC queries,
WAN gossip to other datacenters, and forwarding queries to leaders or remote datacenters.
* Datacenter - A datacenter seems obvious, but there are subtle details such as multiple
availability zones in EC2. We define a datacenter to be a networking environment that is
@ -47,13 +47,13 @@ the public internet.
the elected leader as well as agreement on the ordering of transactions. Since these
transactions are applied to a FSM, we implicitly include the consistency of a replicated
state machine. Consensus is described in more detail on [Wikipedia](http://en.wikipedia.org/wiki/Consensus_(computer_science)),
as well as our [implementation here](/docs/internals/consensus.html).
and our implementation is described [here](/docs/internals/consensus.html).
* Gossip - Consul is built on top of [Serf](http://www.serfdom.io/), which provides a full
[gossip protocol](http://en.wikipedia.org/wiki/Gossip_protocol) that is used for multiple purposes.
Serf provides membership, failure detection, and event broadcast mechanisms. Our use of these
is described more in the [gossip documentation](/docs/internals/gossip.html). It is enough to know
gossip involves random node-to-node communication, primarily over UDP.
that gossip involves random node-to-node communication, primarily over UDP.
* LAN Gossip - Refers to the LAN gossip pool, which contains nodes that are all
located on the same local area network or datacenter.
@ -62,8 +62,8 @@ located on the same local area network or datacenter.
servers are primarily located in different datacenters and typically communicate
over the internet or wide area network.
* RPC - RPC is short for a Remote Procedure Call. This is a request / response mechanism
allowing a client to make a request from a server.
* RPC - Remote Procedure Call. This is a request / response mechanism allowing a
client to make a request of a server.
## 10,000 foot view
@ -73,7 +73,7 @@ From a 10,000 foot altitude the architecture of Consul looks like this:
![Consul Architecture](consul-arch.png)
</div>
Lets break down this image and describe each piece. First of all we can see
Let's break down this image and describe each piece. First of all we can see
that there are two datacenters, one and two respectively. Consul has first
class support for multiple datacenters and expects this to be the common case.
@ -85,9 +85,9 @@ and they can easily scale into the thousands or tens of thousands.
All the nodes that are in a datacenter participate in a [gossip protocol](/docs/internals/gossip.html).
This means there is a gossip pool that contains all the nodes for a given datacenter. This serves
a few purposes: first, there is no need to configure clients with the addresses of servers,
a few purposes: first, there is no need to configure clients with the addresses of servers;
discovery is done automatically. Second, the work of detecting node failures
is not placed on the servers but is distributed. This makes the failure detection much more
is not placed on the servers but is distributed. This makes failure detection much more
scalable than naive heartbeating schemes. Thirdly, it is used as a messaging layer to notify
when important events such as leader election take place.
@ -97,8 +97,8 @@ processing all queries and transactions. Transactions must also be replicated to
as part of the [consensus protocol](/docs/internals/consensus.html). Because of this requirement,
when a non-leader server receives an RPC request it forwards it to the cluster leader.
The server nodes also operate as part of a WAN gossip. This pool is different from the LAN pool,
as it is optimized for the higher latency of the internet, and is expected to only contain
The server nodes also operate as part of a WAN gossip pool. This pool is different from the LAN pool,
as it is optimized for the higher latency of the internet, and is expected to contain only
other Consul server nodes. The purpose of this pool is to allow datacenters to discover each
other in a low touch manner. Bringing a new datacenter online is as easy as joining the existing
WAN gossip. Because the servers are all operating in this pool, it also enables cross-datacenter requests.
@ -110,8 +110,8 @@ connection caching and multiplexing, cross-datacenter requests are relatively fa
## Getting in depth
At this point we've covered the high level architecture of Consul, but there are much
more details to each of the sub-systems. The [consensus protocol](/docs/internals/consensus.html) is
At this point we've covered the high level architecture of Consul, but there are many
more details for each of the sub-systems. The [consensus protocol](/docs/internals/consensus.html) is
documented in detail, as is the [gossip protocol](/docs/internals/gossip.html). The [documentation](/docs/internals/security.html)
for the security model and protocols used are also available.

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@ -10,8 +10,8 @@ description: |-
Consul relies on both a lightweight gossip mechanism and an RPC system
to provide various features. Both of the systems have different security
mechanisms that stem from their designs. However, the goals
of Consuls security are to provide [confidentiality, integrity and authentication](http://en.wikipedia.org/wiki/Information_security).
mechanisms that stem from their designs. However, the overall goal
of Consul's security model is to provide [confidentiality, integrity and authentication](http://en.wikipedia.org/wiki/Information_security).
The [gossip protocol](/docs/internals/gossip.html) is powered by [Serf](http://www.serfdom.io/),
which uses a symmetric key, or shared secret, cryptosystem. There are more
@ -19,10 +19,11 @@ details on the security of [Serf here](http://www.serfdom.io/docs/internals/secu
The RPC system supports using end-to-end TLS, with optional client authentication.
[TLS](http://en.wikipedia.org/wiki/Transport_Layer_Security) is a widely deployed asymmetric
cryptosystem, and is the foundation of security on the Internet.
cryptosystem, and is the foundation of security on the Web, as well as
some other critical parts of the Internet.
This means Consul communication is protected against eavesdropping, tampering,
or spoofing. This makes it possible to run Consul over untrusted networks such
and spoofing. This makes it possible to run Consul over untrusted networks such
as EC2 and other shared hosting providers.
~> **Advanced Topic!** This page covers the technical details of

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@ -64,9 +64,9 @@ systems to be built that require an operator to intervene in the
case of a failure, but preclude the possibility of a split-brain.
The final nuance is that sessions may provide a `lock-delay`. This
is a time duration, between 0 and 60 second. When a session invalidation
is a time duration, between 0 and 60 seconds. When a session invalidation
takes place, Consul prevents any of the previously held locks from
being re-acquired for the `lock-delay` interval; this is a safe guard
being re-acquired for the `lock-delay` interval; this is a safeguard
inspired by Google's Chubby. The purpose of this delay is to allow
the potentially still live leader to detect the invalidation and stop
processing requests that may lead to inconsistent state. While not a
@ -79,7 +79,7 @@ mechanism by providing a zero delay value.
Integration between the Key/Value store and sessions are the primary
place where sessions are used. A session must be created prior to use,
and is then referred to by it's ID.
and is then referred to by its ID.
The Key/Value API is extended to support an `acquire` and `release` operation.
The `acquire` operation acts like a Check-And-Set operation, except it
@ -93,7 +93,7 @@ since the request will fail if given an invalid session. A critical note is
that the lock can be released without being the creator of the session.
This is by design, as it allows operators to intervene and force terminate
a session if necessary. As mentioned above, a session invalidation will also
cause all held locks to be released. When a lock is released, the `LockIndex`,
cause all held locks to be released. When a lock is released, the `LockIndex`
does not change, however the `Session` is cleared and the `ModifyIndex` increments.
These semantics (heavily borrowed from Chubby), allow the tuple of (Key, LockIndex, Session)
@ -103,7 +103,7 @@ is incremented on each `acquire`, even if the same session re-acquires a lock,
the `sequencer` will be able to detect a stale request. Similarly, if a session is
invalided, the Session corresponding to the given `LockIndex` will be blank.
To make clear, this locking system is purely *advisory*. There is no enforcement
To be clear, this locking system is purely *advisory*. There is no enforcement
that clients must acquire a lock to perform any operation. Any client can
read, write, and delete a key without owning the corresponding lock. It is not
the goal of Consul to protect against misbehaving clients.

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@ -8,8 +8,8 @@ description: |-
# Run the Consul Agent
After Consul is installed, the agent must be run. The agent can either run
in a server or client mode. Each datacenter must have at least one server,
After Consul is installed, the agent must be run. The agent can run either
in server or client mode. Each datacenter must have at least one server,
although 3 or 5 is recommended. A single server deployment is _**highly**_ discouraged
as data loss is inevitable in a failure scenario. [This guide](/docs/guides/bootstrapping.html)
covers bootstrapping a new datacenter. All other agents run in client mode, which
@ -114,10 +114,11 @@ By gracefully leaving, Consul notifies other cluster members that the
node _left_. If you had forcibly killed the agent process, other members
of the cluster would have detected that the node _failed_. When a member leaves,
its services and checks are removed from the catalog. When a member fails,
its health is simply marked as critical, but is not removed from the catalog.
its health is simply marked as critical, but it is not removed from the catalog.
Consul will automatically try to reconnect to _failed_ nodes, which allows it
to recover from certain network conditions, while _left_ nodes are no longer contacted.
Additionally, if an agent is operating as a server, a graceful leave is important
to avoid causing a potential availability outage affecting the [consensus protocol](/docs/internals/consensus.html).
See the [guides section](/docs/guides/index.html) to safely add and remove servers.
See the [guides section](/docs/guides/index.html) for how to safely add
and remove servers.

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@ -19,9 +19,8 @@ two node cluster running.
## Defining Checks
Similarly to a service, a check can be registered either by providing a
[check definition](/docs/agent/checks.html)
, or by making the appropriate calls to the
[HTTP API](/docs/agent/http.html).
[check definition](/docs/agent/checks.html), or by making the
appropriate calls to the [HTTP API](/docs/agent/http.html).
We will use the check definition, because just like services, definitions
are the most common way to setup checks.

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@ -14,12 +14,12 @@ Consul, but didn't show how this could be extended to a scalable production
service discovery infrastructure. On this page, we'll create our first
real cluster with multiple members.
When starting a Consul agent, it begins without knowledge of any other node, and is
an isolated cluster of one. To learn about other cluster members, the agent must
_join_ an existing cluster. To join an existing cluster, it only needs to know
about a _single_ existing member. After it joins, the agent will gossip with this
member and quickly discover the other members in the cluster. A Consul
agent can join any other agent, it doesn't have to be an agent in server mode.
When a Consul agent is started, it begins without knowledge of any other node,
and is an isolated cluster of one. To learn about other cluster members, the
agent must _join_ an existing cluster. To join an existing cluster, it only
needs to know about a _single_ existing member. After it joins, the agent will
gossip with this member and quickly discover the other members in the cluster.
A Consul agent can join any other agent, not just agents in server mode.
## Starting the Agents
@ -78,7 +78,7 @@ agent-one 172.20.20.10:8301 alive role=consul,dc=dc1,vsn=2,vsn_min=1,vsn_m
agent-two 172.20.20.11:8301 alive role=node,dc=dc1,vsn=2,vsn_min=1,vsn_max=2
```
-> **Remember:** To join a cluster, a Consul agent needs to only
-> **Remember:** To join a cluster, a Consul agent only needs to
learn about <em>one existing member</em>. After joining the cluster, the
agents gossip with each other to propagate full membership information.

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@ -62,7 +62,7 @@ $ curl http://localhost:8500/v1/kv/?recurse
Here we have created 3 keys, each with the value of "test". Note that the
`Value` field returned is base64 encoded to allow non-UTF8
characters. For the "web/key2" key, we set a `flag` value of 42. All keys
support setting a 64bit integer flag value. This is opaque to Consul but can
support setting a 64-bit integer flag value. This is opaque to Consul but can
be used by clients for any purpose.
After setting the values, we then issued a GET request to retrieve multiple
@ -115,5 +115,5 @@ returning the current, unchanged value. This can be used to efficiently wait for
key modifications. Additionally, this same technique can be used to wait for a list
of keys, waiting only until any of the keys has a newer modification time.
This is only a few example of what the API supports. For full documentation, please
reference the [HTTP API](/docs/agent/http.html).
These are only a few examples of what the API supports. For full
documentation, please see the [HTTP API](/docs/agent/http.html).

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@ -67,9 +67,9 @@ service using either the DNS or HTTP API.
Let's first query it using the DNS API. For the DNS API, the DNS name
for services is `NAME.service.consul`. All DNS names are always in the
`consul` namespace. The `service` subdomain on that tells Consul we're
querying services, and the `NAME` is the name of the service. For the
web service we registered, that would be `web.service.consul`:
`consul` namespace. The `service` subdomain tells Consul we're querying
services, and the `NAME` is the name of the service. For the web service
we registered, that would be `web.service.consul`:
```text
$ dig @127.0.0.1 -p 8600 web.service.consul