說到Key / Value 大家第一想到的應該也跟我一樣 "etcd" 或是 "ZooKeeper", 官網也有一篇文章介紹，google也有不少比較表，這邊就不再英翻中或是換句話說了。
今天會介紹Consul kv的使用方式，包含get, put, import ,export 以及 delete.

Key / Value

目的: 將需要動態配置的資料存放於此，透過Consul 提供HTTP API的呼叫來達到即時性。
Value: Value的建議最大值在512kb, 可以透過參數kv_max_value_size來調整，文件有備註說明，不適當的值可能會影響效能或是發生問題。
Key: Key 的命名原則上不受限制，但官方建議使用URL的安全字元[a-zA-Z0-9-_]並排除"/", 也避免使用*, ?, ', % 容易在http api與shell scripts上出錯。 "/" 會被使用在區分目錄結構上。

Note: 若無特別的配置，在跨DC的K/V是獨立於各數據中心的，但可以透過consul-replicate tool來定期複製資料。

新增

假設要設定ERP系統的http session參數，可以這樣子設定

$ consul kv put erp/http/minsession 1
Success! Data written to: erp/http/minsession

consul kv put erp/http/maxsession 50
Success! Data written to: erp/http/maxsession

查詢

$ consul kv get erp/http/minsession
1

$  consul kv get erp/http/maxsession
50

刪除

$ consul kv delete erp/http/minsession
Success! Deleted key: erp/http/minsession

修改

要修改資料與新增相同，Consul會直接覆蓋舊的資料。

$ consul kv put erp/http/maxsession 100
Success! Data written to: erp/http/maxsession

列出所有K/V

$ consul kv get -recurse
erp/http/maxsession:100
erp/http/minsession:1
ithome/http/maxsession:123
ithome/http/minsession:20
order/http/maxsession:100
order/http/minsession:10

列出部分K/V

例如列出order開頭的

$ consul kv get -recurse order/
order/http/maxsession:100
order/http/minsession:10

匯出K/V

這邊會看到除了key, vale外，還會有flag, 因為在寫入時沒有指定flag，所以都是0.
Value的值怎麼怪怪的，這是被base64編碼過了，需要再解密人類才能看得懂。

$ consul kv export
[
        {
                "key": "erp/http/maxsession",
                "flags": 0,
                "value": "MTAw"
        },
        {
                "key": "erp/http/minsession",
                "flags": 0,
                "value": "MQ=="
        },
        {
                "key": "ithome/http/maxsession",
                "flags": 0,
                "value": "MTIz"
        },
        {
                "key": "ithome/http/minsession",
                "flags": 0,
                "value": "MjA="
        },
        {
                "key": "order/http/maxsession",
                "flags": 0,
                "value": "MTAw"
        },
        {
                "key": "order/http/minsession",
                "flags": 0,
                "value": "MTA="
        }
]

base64 解密，以order/http/minsession為例。

$ base64 --decode <<< "MTA="
10

匯出部分K/V

$ consul kv export order/
[
        {
                "key": "order/http/maxsession",
                "flags": 0,
                "value": "MTAw"
        },
        {
                "key": "order/http/minsession",
                "flags": 0,
                "value": "MTA="
        }
]

匯入K/V

匯入的話也需先將value加密為base 64,先將兩個值加密

$ base64 <<< "66"
NjYK

$base64 <<< "88"
ODgK

編輯要匯入的json file

# pay.json

[
        {
                "key": "pay/http/maxsession",
                "flags": 0,
                "value": "ODgK"
        },
        {
                "key": "pay/http/minsession",
                "flags": 0,
                "value": "NjYK"
        }
]

執行匯入

$ consul kv import @pay.json
Imported: pay/http/maxsession
Imported: pay/http/minsession

查詢看看是否成功

$ consul kv get pay/http/maxsession
88

$ consul kv get pay/http/minsession
66