Document formats :

{
    id: '{UUID}', // PRIMARY
    action: '{user action: join|leave}',
    content: '{text content}',
    created: '{timestamp}'
}

Example :

{
    id: '27961a0e-f4e8-4eb3-bf95-c5203e1d87b9',
    action: 'join',
    content: 'New user!'
    created: '1519639337230'
}